They are ok as long as you have a thermostat! I would definitely recommend you give them UV light too!
With my diamonds, I keep them in a large mesh enclosure in my reptile room and I don't use any heating, just a UV light, and the are healthy as could be! But I probably wouldn't recommend keeping them like that down there as it is a fair bit cooler.
But anyway, with diamonds, give them a big enclosure with plenty of ventilation, keep them a bit cooler than you would a carpet, give them UV light and they should thrive!
diamonds arn't like other snakes, don't treat them the same. you want the ambient temp for a diamond in the warm end to be abt 29 degrees..........and the basking spot right under the lights can be a little warmer, but ours with sunshine is only abt 30 degrees, not much different at all. the cooler end drops to 23/24 degrees which is where she spends alot of her time, which goes to show they don't want or need the heat, of 30 and above. this is what i would be doing.