I only had staked vexPOLYCUB. I chose POLYCUB. It worked fine.

And yes you can burn the staked tokens. I burned vexPOLYCUB by sending them to the same address as for burning CUB or POLYCUB. Just put the transaction link for the burning of said staked tokens

I would check on discord and open a ticket to be sure, but it worked for me. . I may be giving bad advice :-) So check with someone else