No. The GPS you will not be able to hear over the speakers.
I recently got a Magellan 4250. (bluetooth works great BTW) But even if you plug the cable into the AUX, I did NOT hear it over the speakers.
(I Dont have BMW bluetooth option)
OP: If you have BMW bluetooth, why are you looking to get a GPS with bluetooth???
2015 335xi | Mineral Grey Metallic | Black Dakota Leather | NAV | SportLine | ZPP | ZDA | ZCW | Munich Build
Retired: 2008, 2011, 2013 328xi