Hedgies are highly scent oriented. They have big sniffers and tiny lungs. They seem to be prone to upper respiratory infections. For that reason, I wouldn't recommend having a highly scented environment. I suppose a candle here or there wouldn't be terribly bad, but I can't really imagine one of those plug-ins. They're pretty strong. And hedgie would be trapped in his cage where he couldn't escape the scent/weird chemicals in the air.
Personally, I try and make things as clean/scent-free as possible... eg, no candles, air fresheners, use the scent-free/dye-free detergent on their fleece, have a HEPA filter running all the time, etc... I suppose the HEPA filter might be going overboard to plenty of folks. But I try and do what I can to do good things for these little quilled ones.
Right about the tea-tree. Keep away from that. Mint should be okay. Again, don't overdo it. A little bit can go a long way for a hedgie.
And, of course, say you light up a candle, watch hedgie... if he's huffing or otherwise looking disturbed, that'll be a big clue that it's a no-go for him.
