Telerik forums are not based on Sitefinity's implementation for Forums. Actually Sitefinity forums do not use pages.You can create a custom breadcrum and get the forum, thread, post by using the IDs passed to the query string when you go to a post or forum. You should work with forums API.
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items