He came in to replace Brian Wilson when he didn't want to tour anymore. First song he's audible in is "California Girls". He left, came back, and now tours as "The Beach Boys" with Mike Love. To me, calling yourselves "the Beach Boys" without a Wilson Brother onstage is like Ringo Starr billing his group "The Beatles."
Here's his Wikipedia biography.
Decide for yourself, but if it's accurate, it appears he has sufficient involvemdnt to be called a Beach Boy.
http://en.wikipedia.org/wiki/Bruce_Johnston
Biography
Bruce Johnston grew up on the West side of Los Angeles in Brentwood and Bel-Air. His adoptive father was president of the Owl Rexall Drug Company in Los Angeles after moving from Walgreens in Chicago. Bruce attended private school in Los Angeles and also studied classical piano in his early years. In high school, Johnston switched to contemporary music. He performed in a few 'beginning' bands during this time and then moved on to working with young musicians such as Sandy Nelson and Phil Spector. Soon Johnston began backing people such as Ritchie Valens, the Everly Brothers, and even Eddie Cochran. In 1959 while still in high school, Johnston arranged and played on his first hit record called "Teenbeat" by Sandy Nelson. The single record reached the Billboard Top Ten chart.
In 1963, Johnston started his record production career at Columbia Records with his friend Terry Melcher. The first artist they both produced was a group called The Rip Chords. By the time Johnston and Melcher were producing the million selling "Hey Little Cobra," a knockoff of the Beach Boys car song vocal style, they also wound up singing every layered vocal part for the recording. The two of them made a few recordings as Bruce & Terry, but Terry Melcher began to focus more on his production career (The Byrds, Paul Revere and The Raiders). On April 9, 1965, Johnston joined the Beach Boys replacing Glen Campbell who was playing bass on the road and singing Brian Wilson's vocal parts. Johnston didn't start playing bass until his first tenure with the Beach Boys, and the very first vocal recording Johnston made as one of the Beach Boys was California Girls.
Johnston subsequently would decide to leave the band after the Surf's Up album, then return. However, throughout the 1970s he would assist and guest on each album the band released. At Brian Wilson's request, Johnston officially rejoined the band for the L.A. (Light Album) sessions in 1978. He also was asked to produce many of the tracks for the L.A. (Light Album).
Johnston is frequently credited as one of the original greatest supporters of the Beach Boys' 1966 signature album Pet Sounds. He flew to London in May 1966 and played the album for John Lennon and Paul McCartney. He wrote several Beach Boy songs, notably, "Disney Girls" (1971), which was covered by both Captain & Tennille and Art Garfunkel. As a songwriter, he wrote the Billboard number one, Barry Manilow hit ("I Write the Songs") for which he won a Grammy. "I Write The Songs" has been recorded by over two hundred artists (including Frank Sinatra) and it currently has a cumulative singles/albums worldwide sales figure of twenty-five million copies. In addition, Johnston wrote backing vocal arrangements and also sang on the recordings for Elton John's "Don't Let The Sun Go Down On Me" and Pink Floyd's album The Wall.
Johnston is still a member of the touring version of The Beach Boys, performing 170 concerts a year. Despite Bruce's long involvement with the band he no longer has a full membership in BRI having traded his shares (but not his artist royalties) back in 1972. Johnston still retains his equal ownership of the band's ASCAP publishing company, Wilojarston, and is the only member of the band to have earned a Song of the Year Grammy.
Or calling yourself CCR without a Fogerty. Oh wait, that almost happened...