I was wondering, is it possible to get the YCS Gauss Rifle first and then use the Auto-Doc to switch to Wild Wasteland and then get the Alien Blaster?

No, it isn't. You'll still get the merc camp even if you turn on WW, since the cell was already saved (due to you visiting it.)

according to fallout wiki you can see every WW event even if you visted that area before, take perk at Sink and go back although i cannot confirm this as I haven't finished OWB on that Chr yet

However the alien blaster is not a WW event, no symbol comes up in corner so you it will be the merc camp