yes.
as long as 10 mil plastic vapor barrier
is continuous on ground of crawlspac.
mastic seal all duct connections, plenum
connections, returns and supply boxes
into house.

where are you building
and how are you conditioning the crawlspace?

best of luck.

Location of site is northern Illinois. HVAC contractor will engineer system to supply sufficient make-up air to crawlspace with return also, to maintain crawlspace at same temp as living space above, all year round.

Would subslab insulation be appropriate? Trying to maintain this space at 70 degrees will actually lose a decent amount of heat to the ground thru an uninsulated slab.

I'm sure it would be a great idea if not contraindicated. Lots of builders here are using a modular polystyrene block/form that insulates and, I think, incorporates the moisture barrier.

Just a note-polystyrene has been listed as a suspected carcinogen by the American Cancer Society since 2010 due to styrene leaching and off gassing. It is also a neurotoxin. I have smelled polystyrene and it produces an awful off gas. I would never consider it in my home.

http://eco-panels.com/blog/63-eps-as-a-carcinogen.html

You need a plastic vapour barrier OVER a concrete floor? I would have assumed there was a moisture barrier under the concrete, and that would suffice.

Where I am, Interior British Columbia, basement floors are bare concrete, and if finished, have carpet and regular underlay, or some sort of hardwood or laminate flooring with some sort of underlayment... but nothing that would really comprise a true vapour barrier.

A lot of the time, basement floor formwork is polystyrene, so it's insulated and moisture-proofed at the same time.