Is it possible to share wolves with other players on multiplayer servers?

I believe that once they have their leashes on them, they cannot be re-tamed, so you're going to have to find a new wolf with your friends, and make sure that they have the bones instead

This method I have found to work, but you have to have sufficient permission on the server to access the entitydata command.

Stand near the wolf you'd like to transfer, (it is helpful to have him sitting), and type the following command:

/entitydata @e[type=Wolf,r=5] {OwnerUUID:yourFriend'sUUID}

And voila! In order to find your friend's UUID, http://mcuuid.net/ is a helpful website.

If you and your friend both have a wolf, whoever's is put into love mode first, that will be the owner I the baby, so this is an effecient way to make a large wolf pack.