If I'm imagining what you're saying correctly (basically you just hang the bag in the pot through the boil, and dump your hops in it when it's time, and then at the end pull it out so you don't have to strain them out or something), it should work just fine, although as you boil the bag is going to want to keep lifting up unless it's awfully heavy. I'm not positive what a hop spider is, I suppose I could look it up but I'm feeling lazy, lol.
I basically used to do exactly what you're proposing though - I'd clamp a paint strainer bag to the rim of the pot in a couple places and dump my hops in as I boiled. Thing is, if you're using whole leaf hops you'll be surprised how quickly the bag gets pretty full. I still do my hop additions in paint strainer bags (tied closed and tossed in) so they've got plenty of room to move around in there while boiling, and I only put a MAX of 3 oz in one. Be sure all the hops will be able to make contact with liquid if they're whole leaf - pack them in too tight and you may find the center still dry at the end.