Would a hack saw with the right blade work/be a safer way to go? Then after Last question is always the dumbest but I got to ask... do I take the fender off the bike an put it in a vise while cutting or can I cut it while on the bike? (I dont have a benchmounted vise so thats why I ask. I'm assuming I'll have to take it off.)
Yes. This is my preferred way. It's hard to make nice flowing lines with a dremel - much easier with hacksaw and files, then emery cloth to smooth things out.