I have not bought hydrangeas bare root but I can see why they do that (less shipping costs). Hydrangeas will have some small roots near the surface and maybe this is the case here. However, I really would have expected some visible roots of some size in each specimen. Just where did you buy this anyway? I would call them back to confirm all is well and just so they (and you) have a note that you called... in case the plants do not make it!

Note: I assume they did not send you a specimen of Viburnum also called Snowball Bush.

H. paniculata should have some white fleshy roots.
If your 2' PGs have 3-4 of such roots and they are at least 6-8" in lenghts plants most likely will be fine. If not...I'd be start looking for return/refund.