Gospel Star Israel Houghton Vouches for Joel Osteen

Joel Osteen ain't lying about not being able to open his megachurch earlier to Houston flood victims ... this according to the gospel star who worked with Joel for years.

We got Grammy winner Israel Houghton Tuesday night at Catch and asked what he made of the backlash Joel's been catching for turning away flood evacuees on Monday, before finally opening Lakewood Church on Tuesday.

Israel was a church member and performed there for 15 years -- and assured us he knows the "real deal" ... as he backed up Joel's word that the church was too flooded.