Yes, and no.
It was the first completed Mormon temple where that happened.
And it was the first dedicated Mormon temple where that happened.
But to show you that a Mormon temple doesn't really need an official “dedication” for that to happen, read from an official Mormon Church Doctrines & Covenants Student Manual (1981, 2000):
”The first baptisms for the dead in the uncompleted Nauvoo Temple were initiated Sunday, 21 November 1841 (see History of the Church, 4:454).” (p. 314)
(Btw, the Mormon “scriptural” root for Mormon temple dedications is Doctrine & Covenants 109 when Joseph Smith dedicated the Kirtland, Ohio temple on March 27, 1836...these days, the LDS Church will hold public “open houses” when a new temple is built; but after the open house, the temple is cleaned literally and “spiritually.” In order for Mormons entering “the threhold of the Lord's house” to “feel thy power” (D&C 109:13), all pagan germs are exorcised with a Smith-like dedication prayer:
”And that no unclean thing shall be permitted to come into thy house to pollute it.” (D&C 109:20)
And that is why no non-Mormons and no Mormons without a temple recommend can enter into a Mormon temple after the open house period; Joseph Smith's temple-segretation prayer tradition is carried on to this very day!
They built the temple in Kirtland...The Saints lost the Kirtland Temple—that was to be something of a pattern for that generation. The Church does not have the Kirtland Temple now.” (Lds "apostle" Boyd K. Packer, The Holy Temple, p. 174, Bookcraft, 1980)
Mr. Packer, what do you mean a “pattern?”
Packer elaborates:
* Aug. 3, 1831, Mormons dedicate temple at Independence, Jackson County, Missouri; yet... “The temple was never constructed. When the Saints were expelled from that area...in 1833 the site fell into other hands. Some day...that site will be fully reclaimed and the house of the Lord built as we have been commanded to do it.” (Packer, p. 174) [Wait a minute, Mr. Packer. What do you mean “Some day...?” Isn't Independence, MO, rather “built up” by 2014? Doesn't the Mormon “prophesy” by Joseph Smith, given Sept. 22-23, 1832, portend that “Which city shall be built, BEGINNING at the temple lot...” (Doctrine & Covenants 84:3)...Furthermore, didn't Smith prophesy of this phantom “temple” that: “Verily this is the word of the Lord, that the city New Jerusalem shall be built by the gathering of the saints, BEGINNING AT THIS PLACE, EVEN THE PLACE OF THE TEMPLE, WHICH TEMPLE SHALL BE REARED IN THIS GENERATION. FOR VERILY THIS GENERATION SHALL NOT ALL PASS AWAY UNTIL AN HOUSE SHALL BE BUILD UNTO THE LORD... (D&C 84:4-5)...So, Joseph lied in this prophesy? And you, Mr. Packer, deliberately ignore Smith's twice usage of the word “beginning?”]
* July 3, 1837, ground for a temple was broken at Far West, MO and cornerstones laid for it, 176 years ago today –July 4, 1838. According to Packer: ”Nothing further was done until April 26, 1839, when the Twelve Apostles, in fulfillment of a revelation, quietly held a conference on the temple site and as a gesture rolled a large stone up to one of the corners as a symbol of beginning construction on the temple. The temple, which would have been 110 feet long and 80 feet wide according to the plan, was NEVER built.” [Wait a minute, Mr. Packer. It was never built...so the Mormon god was “into” empty symbolism and aborted “gestures?”]
* Early 1840s: “Much of what happened at Kirtland was repeated in Nauvoo. We built a temple in Nauvoo. It was destroyed...In Nauvoo the temple was defiled and destroyed.” (Packer, p. 174) [Wait a minute, Mr. Packer! I thought Joseph Smith prophesied on Jan. 19, 1841 that “my servant Joseph and his seed after him {shall} have place in that house, from generation to generation, forever and ever, saith the Lord. And let the name of that house be called Nauvoo House...” (D&C 124: 59-60)...Hmm...I guess phrases like “generation to generation” re: Smith's personal household and “forever and ever” must have different meanings to Mormons and their leaders, eh?]
Bottom line? Joseph Smith prophesied falsely in D&C 84:3-5 and 124:59-60. A thief who steals a few times is a thief; a murderer who murders a few times is a murderer; and a prophet who prophesies a few times “in the Name of the Lord” is a false prophet!
1. Joseph Smith primarily left Kirtland Ohio because the bank he started had failed and he bailed out.
2. The Mormons would like to blame Missouri mobs for the failure of the temple in Independence, MO, yet even the official Mormon Church curricula, Doctrine and Covenants Student Manual (1981/2000), says that besides the “mobs” another reason existed: ”...AND because the Saints at that time had not kept the commandments as they should (see D&C 105:1-9)” So even Mormon leaders blame the Mormon people!
3. The Mormons were in the Salt Lake Valley for about 30 years before the St. George temple was dedicated. (What took so long for those early Utah "pioneer Mormons" to be faithful to the Mormon gods' commands?)
Actually as I understand it it was the first Temple to perform “endowments” Mormons baptism for the dead is not the same thing as endowments. The baptisms have to be performed before the endowments. Living people received their own endowments in the Nauvoo temple but not for dead, the article is correct in that endowments didn't happen for the dead until St. George.
If I were to join the church I could perform baptisms the next day in the temple but would still have to wait a year for my endowments or for doing the endowments for the dead. A person has to have their own endowments before they can do it for the dead.