No, hardness testing is not required to confirm adequate PWHT of P-1 material >19mm, per B31.3. Per 331.1.7(a), if no hardness limit is listed in the table, testing is not required.
However, it is a VERY good idea to do a few spot hardness tests of PWHT'd welds. Makes everybody 'happy', by proving that your PWHT was proper. The number you are looking for is Brinnell Hardness 'BHN' of 200 or less.