This is actually a loaded question with many things to consider. The main question in my mind is what kind of traffic is going over this link. Are you just snapping your luns over this link to a standby array? Are you running live data in a synchronous environment?
I would be comfortable snapping data over a wireless link, but not comfortable running synchronous data.
The reality of the fact is that wireless has signal loss, and events due to weather. If you are doing gigabit at 30 miles (though, the fastest I have seen at that range is oc-12 speeds) you are going to be up in the high microwave range, which tends to react to precipitation and moisture in the air. Along with being on a high tower which can get affected by winds.
If you have redundant paths, and are snapping this will not be a problem, as you will probably just have to re-initialize the snapshot in a worst case scenario.
If you are doing synchronous writes, you are just asking for a giant headache.
--Colin
http://www.2cups.com