<p>I've heard that using hairspray is useful for keeping the 3D objects from peeling off of the bed, but every example I have seen where someone uses hairspray, they use it on a glass bed.</p>

<p>Is it okay to use it on a metal bed as well?</p>

Do you mean bare metal or metal with some film on top? You can apply hair spray to bare metal, but you will have troubles cleaning it off. Solvents do not evaporate hair spray, they only turn it into thick sticky goo you will need to clean off. I recommend that you try glue stick or even beer (seriously) before hair spray.
You should also know that
any
adhesive is required only when your printer has bed leveling issues. After I finally dealt with bed leveling, I print ABS, and even ABS/PC mix (nasty) without any adhesive, on a bare kapton film over a metal bed. I rub it with alcohol before printing.