Hi,
Yes it is. I have great luck transplanting this time of year. In fact, you don't have to worry about watering as much as earlier in the year since the soil stays moist longer in the cool temps.
Remy

Thanks! I would hate to think I was just dooming my transplants to an inevitable frozen death.

Given specifically what you are planting, whether or not this is a problem will depend on the size of the transplants. Both hosta and daylilies (and siberian iris - which is how I know this) have fairly narrow root systems. Small divisions can have a hard time rooting themselves into the ground, and be squeezed out like toothpaste from frost heave. Usually, garden divisions are fairly large, with most of the original, spreading root system still in place. I have on occasion planted daylilies as single fans, and I wouldn't do that this time of year.

Don't drown them. Check the soil moisture before watering.