I think this is a great idea. Players who help out in the help chat are awesome, but I think rewarding those players chosen via whatever voting system with a small icon beside their name or changing the color of their name is not a good idea, especially if the voting system is biased.
Don't get me wrong, they do deserve recognition, but that can be done with other things like an icon on their trainer card that is rewarded privately and not in the chat where anyone can see.
If i'm going to be honest, i'm just afraid that this "Icon" or "Badge" beside their names will get to their heads and make them feel better than anyone else that wants to help in the help chat, giving a feeling of superiority to those who have it.
That and I've also seen a few active helpers in help chat act passive-aggressive towards a mod that's trying to answer, for no reason at all. Yes, I've seen that happen more times than I needed to unfortunately, and i'm sure others have as well.
To add to all that, this may potentially make the help chat a competition to see who could answer the most questions, or to see who can answer the fastest, and not out of willingness to help.
I'm aware that not everyone is like this though, and that they genuinely want to help. Of course, this is only my opinion on what I think about the suggestion and rewards. Please don't take it the wrong way.
TL;DR : +1 on the voting system as long as it isn't biased, -1 on having icons beside the player name as a reward or type of recognition because of the reasons stated above.
Thanks and have a great day.