Well the key is to measure, of course. The Nashbar fork axle-to-crown of 453mm perfectly matches the extended length of my original suspension fork, yes for 26" wheels. That one you linked only has an axle-to-crown of 390mm, barely taller than the 700x35c tire itself. So yes that would definitely throw a 29er's geometry out of whack.

A suspension fork for a 29er has at least a 500mm axle-to-crown, but the OP really needs to measure and verify before looking for a rigid fork.