Yes, the mechanical webshooters themselves are not an issue.
When it comes to the fluid itself, my main concern is this: I imagine that, in order to fit into the mechanical webshooter, the fluid cartridge itself would have to be fairly small (like the size of a test tube). But in that case, wouldn't it run out fairly quickly? Considering Spider-Man is shooting webs that reach great lengths, he'd have to change cartridges constantly.
Take a water gun, for example. It has a fairly large container to hold the water. Depending on the gun you're using and how many times you pump it, the water will shoot out roughly thirty feet. After a while, the container becomes empty and you have to refill it.
Now take that water gun, decrease the size of the water container to the size of a test tube, pump, and shoot. You'd be out of water probably after the first shot.