Actually, he just has to sense him (not see him). Remember, Luke and Vader could talk to each other without seeing each other. Vader could sense Luke on ships really far away, as well (multiple kilometers).
Also, it has been ages, but Blade is immune to telepathy but I think that's only vampire telepathy. Still, Blade has a really strong will. There's no way a mind trick would work on someone like blade. I know that wasn't contested, but it was just something I thought of.
So, yes, I think that Vader could detect blade from a distance without seeing him. Anakin did it with Padme while being in the middle of an argument with Obi Wan...and he was just a Padawan, then.
Originally posted by jaden101
We know you don't have to see someone to 1: be able to sense them with the force and 2: Be able to locate and use the force to communicate with people. We also know from canon EU that you don't need sight to target things (living or not) with force powers. (Rahm Kota)
STFU, f*ggot. Your stealing my thunder with your ninja fast posts. uhuh