www.kraytracing.com

is there a way to exclude objects from radiosity calculation ?
(if yes, and it's obvious don't laugh )

hmm you can make object unseen by rays. But this will exclude it from all raytracing.
The option to exclude object from only GI is on todo list.

Can you exclude object not to throw caustics?

Not yet.

This would save time.
On the list or...?

Yep...it is on the list...