I have before, and love to use them as a "set" for photo sessions (they're my favorite flowering plant to have in my yard/balcony). But only outside, as they do awful indoors. Yes they have thorns but I haven't seen a chameleon get triped up but them yet, they seem to know what they're doing.
Edit - Even my outdoor cages or free-ranges all have horizontal branches as perches, so the chameleon has the option of sleeping or resting on a thicker, non-thorny branch. But they walk around the bougainvilleas without trouble, it seems.