“The writer was inspired by the Spirit, so we should take it literally unless the text itself indicates otherwise. But why else instantly add ignorance about the grave’s location unless it’s indicating a “tongue-in-cheek” burial?”
No, it was a hidden burial for Satan wanted to use the body of Moses to get Israel to worship him as an idol. Satan contended with Michael over the body and lost.
Several of the pictures show this angelic battle.
One point about Moses and Elijah appearing with Jesus in the Transfiguration: Matt. 17:9 Now as they came down from the mountain, Jesus commanded them, saying, “Tell the vision to no one until the Son of Man is risen from the dead.” (NKJV)
Jesus and Moses and Elijah were all a vision to James, John, and Peter. There is no indication they were there physically or spiritually.
Satan contended with Michael over the body
Jude 9 doesn't specify the nature of their contention: it could indicate there was indeed a body, but Satan could also simply have been demanding to be told its whereabouts, which would accord with Moses' translation--so Jude, and the artists' depiction of the former interpretation, do not appear conclusive to me.
“Tell the vision to no one until the Son of Man is risen from the dead.” (NKJV)
“Don’t tell anyone what you have seen, until the Son of Man has been raised from the dead.” (NIV) Strong's defines the Greek word "horama" (3705) as "a spectacle, vision, that which is seen," which to me rather indicates an actual physical appearance. There is no indication they weren't there physically or spiritually.