Can I cross play against friends on other platforms?

You certainly can :) cross play is supported via the "Random" online play (cueing all versions at the same time will connect all parties - up to 4) and is available across Oculus Quest, Oculus Go, Oculus Rift, Steam, Viveport and Nintendo Switch.

If your whole party are playing on either the Oculus Rift or Oculus Quest you don't have to use the "Random" invite but can instead invite directly using the Oculus friends invite system.