Is this legit Harassment?

[Vahlnir]

I don’t know about strictly jumping around a person as they’re at a placard, but the summoning mounts thing to try to deliberately cover or cause issues with targeting is a reportable and punishable offense. When Palace of the Dead came out, people were summoning their large mounts and planting them on top of the PotD NPC to cause problems. When they were reported, GMs immediately disconnected them from the game. So the other players summoning a mount and obstructing the placard is something they could get in trouble for.

Yeah, when there's competition involved all sorts of people come out of the woodwork. They can potentially resort to some pretty dirty tactics. I saw it a lot in WoW when it came to rare spawns in the open world or for silly things like parking a huge mount on top of a mailbox or important quest NPCs. FF XIV housing is more of a PvP mode than its actual PvP modes, so it's not surprising.