If hard capping is sealing off air line connectors on top of shocks,I suppose you have sealed off any escape route for the shock oil and you should be able to ship them in any position.
However before you uncork them (for whatever reason) I recommend you stand them upright for a few...just to make sure the oil drains back. Like when you lay a refrigerator down to transport.....get the oil back where it belongs before you use it!