Hi, I work at a Saab repair place (internship kinda thing). On Monday, I'll ask the mechanics what they know. What I do know is that GM engines are modified heavily (and sometimes not for the better) before going into Saabs. ex: the 2.5 litre Cadillac Catera engine, which is usually fast, was detuned and fittings were made smaller before being placed in the 00-02 9-5 where it drives like crap.
However, on the positive side, so many Saab parts are GM branded, that with enough effort, a match could likely be made.
PS: The only non Saab GM car I know of with the 2.8 is the low-end Cadillac CTS.