It's very possible. If you think you can get away with it, put plastic bags over doorways so you can hear when/if he moves over them. I also thought of a place where he might still be in the attic. Did you check the eaves? Where the slope of the inside of the roof meets the 'floor' of the attic? He might have gotten himself into a corner. Check near heating vents. Remember: he'll go somewhere warm and tight.

Also, check his tub again. Check all over the rack, check all the heat tape, check behind the rack and on top and everywhere. Check your female's tub. There's no telling where he's managed to go.