Don't do it. Nope.

You'll strip the nipples. It's way easier than you think. Sometimes it even happens with a spoke wrench if it's really tight and you're careless. Pliers are totally asking for trouble since their jaws are not perfectly parallel. I tried it (very carefully, I thought) before I had the right tools, and ruined a few spoke nipples.

Do yourself a favor and get some spoke wrenches. They're cheap. Can get a set of 3 from Performance for $12, and even department stores like Target often have small reversible ones with two sizes for about $3-5. I've used those and they're fine, if a bit harder to grip.