This is an interesting one. I was completely unaware of "Harry Delmar's Revels" until your posting. It is not mentioned by Suskin in "Show Tunes", although he does say "I Can't Give You Anything But Love" became an immediate success after it was performed in"Blackbirds of 1928".
I can find nothing that credits McHugh/Fields for any of the music in "Harry Delmar's Revels". According to the website devoted to Fields, Delmar hated the song and it was cut after opening night, but according to another source, it was cut prior to the opening, http://www.ovrtur.com/show/119780. I don't know if there were public performances of "Revels" before the scheduled opening - tryouts are common now, but I don't know if that was true in 1927 and 1928 and, even if true, whether the practice extended to tryouts for musical revues. So I'm not sure if there ever were public performances of "I Can't Give You Anything but Love" as part of "Harry Delmar's Revels".
I have seen claims - mentioned at the Fields' website, that the song was originally "I Can't Give You Anything but Love, Lindy". In fact, at least the "Jazz Standards" site states that Fields rewrote the lyrics for "Blackbirds". See, http://www.jazzstandards.com/compositions-1/icantgiveyouanythingbutlove.htm. That site also discusses whether McHugh/Fields even wrote the song, as there is some evidence for, and supporters of the claim, that this was a Fats Waller/Andy Razaf composition that Waller sold to McHugh.
So at this point, I'm thinking I'll add a Comment, but I don't think I'll be saying it was originally performed in "Delmar's Revels", although this may be the case.