I am having a hard time distinguishing. Judging by the era it could be a synth. But then again, it could just be a super mwaah fretless. Either way, good song, albeit cheesy.
The high slide at 2.30 gives it away as synth imo, but whomever played it, did a wicked job of getting the fretless vibe down, it's great and played with a bassists approach.
