Hi Eduardo,
you are right, that you need at least the SELECT privilege on SYS.PROCEDURE_PARAMETERS in order to execute the procedures, as the $.hdb interface supports as well table type parameters and the $.hdb api determines the input and output parameters before execution.
However I think that it is no big deal to assign the role RESTRICTED_USER_ODBC_ACCESS to restricted users like the role PUBLIC, which includes the privilege as well, is assigned to all non restricted users.
Regards,
Michael