Do peaches and apricot trees need a "cold time" in order to fruit? Would I be able to have one of these in a pot and take it in the g'house come cold weather and have it fruit? Yeah, I know, should be a dwarf. With being in 4A (close to 4B, but I'm a realist when it comes to this type of thing) I know if the zone chart says 4-8, I'm pushing it.
Depends on how much you warm your greenhouse. If you're not really heating it much and just using it to protect them from the worst of the cold then you should still get enough chill hours for them to fruit. But if you have a greenhouse full of tropicals and you keep it well-heated for them, then it won't get enough chill.
Peaches and apricots are cold climate trees but I don't know how far down on the temperature scale they can go. I remember years ago in France there were stone fruit kept in greenhouses to get early fruit ripening, no idea though what temperature they were kept at. No doubt they were allowed to chill and then kept a bit warmer.
Yeah, doesn't count as chill hours unless it's below 40. I don't know how much effort you're willing to put in, but you could always leave them outside the majority of the time and just put them in the greenhouse or wrap them in burlap or something if you're expecting a day or two of temperatures that would be too cold for them. Either that or pick the most protected side of your house, plant them there, and hope for the best. They might surprise you. Also look around the neighborhood and see if others are growing them, or talk to a reputable local nursery--they can tell you whether they'd have a good chance in your area or not.