Yes, inkscape vectors will work, but I'm pretty sure the photoshop one will not be considered a true vector in the sense that shutterstock means - as Karin points out, you need the illustrator format (illustrator 8 ) - they will accept the image as a .jpg illustration though. I'm pretty sure Perry submitted a bunch of those "PS" vectors and they ended up being accepted, but weren't vectors and had to be converted.
Karin is right that you can do some of the work on a vector in photoshop, but there are some things (like gradients I think) that don't work properly in the PS vector. I created one in PS (seems like ages ago now) and sent it to Lee (striver) to check it because he has illustrator, but the gradients I used came out like blocks of colour not gradients. In using illustrator (uh, very little actually) I found differences in how things work in there. I've still got a vector from "before" I haven't tried to open yet in illustrator (just a practice heart with curls)...should have a look
I purchased Illustrator 9, GoLive, LiveMotion, and InDesign for $80 on e-bay. I didn't want the other programs (they were older versions and I didn't need their uses) but Illustrator 9 was more than suitable for me; since I don't have XP or Vista the newest Illustrator won't run on my computer anyway, and if I feel the need later, I can still upgrade the illustrator package I've got.
It does seem to be a hog on memory though - I've got 3 gb of ram now, but it didn't want to go too fast when I only had 1 gb.
...ignore any typos; I've already fixed a dozen but my eyes are so blurry i can't see right now to fix anymore (eye drops ugh)...going to 'listen' to tv for a while