I am not sure, I would expect as long as the tree doesn't exude anything toxic and that the Hoya vines do not engulf and choke out the tree it would be ok. I remember reading about one tropical grower who had a Hoya vine escape, break off of the main plant, and still keep on going. The post is on houzz, it eventually trailed back down and surprised them with flowers.

I would try to be careful about not letting Hoya loose on the local ecosystem, but if its just a yard shrub and not immediately adjacent to forest probably a non issue.

Hoyas are epiphytic, which means they are harmless to their hosts. It won't hurt your tree to let it climb, but of course if you have a cold snap and have to bring it in, you'll have to whack those vines that go up. They could survive because they typcially set roots in the crevices of trees and may not need the potted mother plant to keep growing. If it was me, once it got big enough that I got tired of keeping the vines from wandering, I'd let it do what it wants. I can't imagine anything more beautiful than a tree with umbels of Hoya flowers to sit under on a warm afternoon!

Denise in Omaha