To me it sounds like a bass guitar with distortion or a fuzz effect. Also since it's a rock band with a bassist it might not be a synth part. Edit: Looking at live videos, it seems he does use a synth [at least in the live version], but I still think you can replicate this with a bass guitar + distortion/fuzz
Most of the fuzz pedals I have used with bass tend to kill some of the low end, so to replicate this track I would use one amp for the clean bass signal and one amp running a distorted or fuzz effect. This way you can hear the attack and the "thump" of the clean bass and still get the fuzz on top. You can probably get close with one amp by keeping the "fuzz" or "gain" levels at or below 50% on your pedal and keep the "tone" knob low so it doesn't kill the lower frequencies.
Some specific info on his bass tone and gear: link 1, link 2
From link 2:
In November 2011, on Twitter a fan asks Kevin Baird: "...a hugh [sic] fan of TDCC and your bass lines,just wanna know which [sic] pedals do u use to get that cool synthy sound :)"
Kevin Baird replies: "gallien and kreuger 1001 head, ampeg 4x10HE, sansamp rb1 rack effect and an mxr bass octave pedal."
"sansamp rb1 rack effect" most closely matches the Tech 21 Sansamp RBI Rackmount Bass Tube Amp Emulator.
So he is probably just using his amp's or the Tech 21 RBI's built-in distortion on this song. The RBI emulates tube distortion, so that likely plays a part in his overdriven tone. It looks like he uses an octave pedal too sometimes, but that's less important to this particular sound. Again, you can replicate it (or come close) with a decent distortion or fuzz pedal. Go to the shop and try some pedals out with your bass, that's the best way to find out.
As far as synth bass guitar goes, have you looked at the EHX Bass Micro Synth?