There is no reason you can't plant as long as they get plenty of sun and you keep them damp (but not drowning). Your potential yield will suffer, but first year hops are hit and miss when it comes to getting enough to do anything with.
The important thing is that if you can still get them, your hops will have a nice start to a second season.
I got some this spring from Great Lakes Hops and they did well considering I forgot to cover them during the last freeze and they nearly died. these guys sell full crowns, not scraggly rhizome sticks.