I think it's not possible to request an upgrade on a ticket booked with a voucher...
Do tickets booked with vouchers book into a "Classic Award" class...?
Frequent Flyer - Using Points - Flight Upgrades - About Flight Upgrades
A voucher is just another form of paying for a revenue fare so it depends on the fare booked - sale/red-e-deal, flexi saver, fully flex etc. You can select the type during the booking process.
I don't know about checking the fare bucket during the voucher booking process, sometimes I've just done an equivalent revenue search for the same flight to correspond with the equivalent fare conditions/price and checked it that way...
http://www.australianfrequentflyer....ent-flyer-program/qf-booking-class-22124.html