I do exactly that. A super light compressor coming in on vocals usually. It's the same as running it through a pre amp that has compression / gate / etc.
Be careful with gate though, coming in. I had a bad experience once where the gate was robbing some of the tail ends of the vocalists notes, and it got recorded that way, and we had to re-record at a less than convenient time.
Just remember whatever you record in with is there forever - you can't remove it later if you decide you don't like it or it's too much.
I even struggle with whether or not I should let the guitarist have reverb on their guitar while recording. Have you ever had to add distortion or gain to a guitar track that has reverb? Worst sound ever!