casters can do their dps at melee range, but you dont call them melee.
Correct, because they're still exclusively using ranged skills and don't gain any dps by going melee.
if the guy sticks to the sab tree for his dps (which most sab rogues do),
You must know different sab rogues than I do, because the sab rogues I know will throw in melee finishers occasionally (through use of annihilation bomb first to detonate spike charges) to get an extra 1.5-2k damage every so often while in melee.
than he QUALIFIES (because yes its a GOOD thing) as ranged dps.
Yes, and he also qualifies as melee dps if he's doing what I described above.
The guy asked... is sab ranged or melee... the answer is ranged... all sab specific dps can and probably should be done at range
I will concede your point that pure sab can easily be classified as a ranged dps soul. However, since the OP has been using sab/sin/nb (a good combination imo), I assumed he was asking about effective sab builds, not just the sab soul, in which case a sab in melee will do more dps than a sab that is staying ranged.