I would say yes. Not ideal, or tactical, but it is a seamanlike maneuver. Like Mark said, don't they do this all the time on monohulls (particularly in match races)?

Scooby, from your responses it seems like you're hell-bent on the windward boat retaining some right to keep the spinnaker trimmed while being headed up. I think it has to be blown it as part of heading up, if that's what's needed to stay upright. Again, the leeward boat is trying to force windward to sail upwind, which is normally done without a spinnaker, so I think the onus is on the windward boat to trim AND maneuver (not just maneuver).

Mike