I've never used them...but according to what I've read the flowers and the branches are not containing any toxins...so it should be ok....but you'll have to decide whether tomriskmit or not yourself!
Keep in mind that lilacs are deciduous, so it's going to be bare & leafless through much of the year.
I'm also not sure how they fare in conditions as humid as a cham enclosure.
Lilacs do best in cool-summer climates and up to USDA plant hardiness zone 7. They are not recommended for hot, humid areas, such as Southern U.S. states in zones 8 or 9.
Keep in mind that lilacs are deciduous, so it's going to be bare & leafless through much of the year.
I'm also not sure how they fare in conditions as humid as a cham enclosure.
I was just hoping to cut costs a bit by finding plants outside, but now thinking about it, I live in Minnesota, so I don’t think there’ll be anything I can take.