can a check be deposited/cashed made payable to the beneficiary in a "for..." account or does another account in that name only be opened?

Assuming your question is strictly limited to checks issued by the U.S. government, anyone appointed as a representative payee is encouraged to open an appropriately named account and deposit the checks. Regardless, the payee may simply choose to cash them.

But can the beneficiary cash a check made payable to himself only off the "for" account

If the account is titled "Ken Golliher FBO John Burnett," and John Burnett asks to cash a check on another bank payable to him (his payroll check, for example), under what theory would you plan to recover the funds from the FBO account if the pay check bounces? John doesn't have access to the FBO account, and Ken didn't endorse the rubber check.

If you want to go ahead and cash the check based on goodwill of the deposit account, go ahead, but do so understanding the risk.