there are two dangers with having a fire close to your shelter, embers, and flare-ups. the biggest factor in these dangers are what you burn, and how you burn it. soft woods like pine and cedar never dry out completely, so they hiss and pop all night. you want to burn the driest hard wood you can find. once you get it going, collapse the fuel, if you keep it tight there will be very little flame, but a whole lot of heat.
point is its perfectly safe, as long as your careful.