sp_plan_dbccdb shows that my dbccdb is indeed large enough and yes, dbcc checkstorage works fine without the rpc.
Ive also tried loopback...sp_dbcc_plandb pubs2 as well as loopback...sp_dbcc_evaluatedb pubs2 and both of them have the same output whether called locally or through rpc.
sp_rpc_setup_check has return status 0, so everything is working ok on that front also.
I havent found in patch notes anything that would indicate there was a change in this matter between 15.0.3 and 15.7, but I will upgrade my test server to 15.7 and try again.
However, even if this will work in 15.7, i would prefer making it work in 15.0.3...