I'd agree I'm not sure a dimmer is your best bet for an incubator BUT I'm sure it can be done. You just have to be sure and set it cooler than you want so if the temps in the room do rise it won't go over 90 degrees.

Tracy Barker talked about using a walled off section of a room for an incubator once and also using the space above the heat coils on a fridge. (back in the olden days) I believe in Africa they just incubate them in huts.

So I'd guess if you set it low enough and monitor it for temperature highs it could be done.....I would't cut those eggs at day 55 or anything like that but if set at say 85 degrees or so I'd imagine they would hatch just fine.

(Again a proportional thermostat with a backup would be better IMO)