OP, go for it, there's no down side. Any layer of protection is beneficial.
If you're sealing reloads, put a small data card in each package. I list caliber, powder and charge, primer and bullet type and date.
It works best on boxed ammo ( no sharp edges ) but will work with loose ammo if you point the bullets inward when arranging them in the bag so they don't peirce the plastic.
Use a quality bag ( Food Saver brand ) not a generic, they just work better.
Also, use a board or other ( stack of paper ) to raise the bag up to the sealer so it stays flat when vacuuming.
I've done lots of ammo this way, particularly .50bmg. It allows me to grab a couple of ten packs to take out to the range instead of lugging a whole can full.