Hmmmmmmmm lets see 30 Amps x 220 Volts = 6600 Watts (thats at unity power factor)
Does the genset also have perhaps a 120 volt 20 amp recerptacle??? if so thats a source of energy available from the genny, but the genny still cant produce more then its rating, regardless which and how may receptacles it serves.
Im not sure about those "other 20 amps" You cant get anymore out of the receptacle then its source can generate, for example if you had a 100 amp receptacle supplied by a generator that could only produce 30 amps, you cant get 100 amps from it just becasue theres a 100 amp CAPACITY receptacle.
Also a 30 amp plug is no guarantee you can pull a full 30 amps from it...The plug is simply a passive connection device, it produses no energy and can only transfer/connect whatever the energy source (the genset) can produce.
Wanna re phrase your question ???