They would have to simulcast on a non trunk frequency (likely VHF) from what I understand. Otherwise, paging on a trunked system won't work from what I can find.
They can page FD's over AWIN by using a console to send out a digital alert to each of the radios individual unit id numbers for that particular fire dept.. This will accomplish the same result as sending out a group page using QCII over the analog system.