Hmm, well basically any type of exercise indeed helps your voice because it makes blood runs better through your body which is good for voice... It also helps your immune system which also helps your voice, then it helps your lung capacity, breathing etc etc..
I also know from my own experience that it does only good for me. I do heavy weight lifting 3 times a week in a gym. I do max 100/110kg on a bench press currently (I had to praise myself a little here hehe:) so I guess that's pretty heavy since I'm 87kg
Basically, I always sing better after gym then before gym..
Now, it might be that you actually dehydrate yourself which is usually common problem in these situations. When you work out in a gym you loose too much water in your body, which might lead to hoarseness. So what you want to do is drink A LOT of water while you are in the gym, which will help you hydrate properly. I guess that's your problem because workout is usually only good for your health... It might only be bad if you do it unready, meaning if you feel tired before you workout, or you try to work much harder then your body is currently allowing you (which can make overfatigue), but I guess that's not the case because you're just starting again now...