There's a difference between what you *can* do and what you *should*
do. A wireless LAN may have sufficient bandwidth to make a direct
synch feasible in terms of time, but because of the extreme
unreliability of wireless connections (which tend to constantly lose
and regain signal), it is not advisable to do a direct synch over
wireless, just as it's not advisable to attempt to use table links
connected to a back end across a wireless link.

You can *do* a direct synch, but it's dangerous, because a direct
synch opens the remote database across the wire. If the connection
drops while that remote database is open, you will corrupt the
remote database and likely lose replicability, which means the
remote database is no longer part of the replica set and can't be
synched. That means you'll end up having to manually recover the
data in it and then create a new replica to replace it.

For a one-time synch, the risk is minimal across wireless. For a
regular synch operation, I would not recommend it as it's simply too
dangerous. The time and cost of implementing indirect replication is
completely worth the effort when compared to the time and cost of
recovering from corruption/loss of replicability (and don't forget
the downtime involved during that recovery).