Hi N.,
First, no, it's not bad to let him cry for a bit once you've been up that many times and determined that nothing is seriously wrong! Honestly... trust your gut! Crying it out can work wonders on infants and toddlers alike and at 8 months, it only took 3 days for my little girl to learn to soothe herself back to sleep... now, at 26 months, she's a champion sleeper, sleeping 7:30-7-8am like clockwork and ONLY crying when something is truly wrong, so I know to respond to her immediately! It's awesome. I read "On Becoming Babywise" and loved that book, it's routine saved me, as a working mom.
Teething time is tough... but if you are giving pain reliever, the symptoms should not be so bad that your little guy can't make it through the night. The trouble is... teething starts bad habits that then get reinforced long after the teething symptoms are gone. My little girl never stopped sleeping through the night just due to teething. But then again, she was a late teether and I had already let her cry it out to reinforce what was going to happen... so teething for us was really not an issue. By the way, even though I'm a "cry it out" mom, I ALWAYS check my girl to be sure she's fine, not ill, not stuck in her crib, not fallen out, etc. I NEVER just let her cry without making absolutely certain that she's fine first. Then, once I'm sure that she's simply crying for mommy's attention, I let her cry it out. It works and it's FAST and you will sleep again, which we all know you need!
Honestly... trust your gut!
K.