This will work. Just remember that if you want to do anything intelligent with the traffic you'll need to have a NAT for each pool member so the BigIP can do traffic management. Another idea is to have another BigIP pair downstream (behind the internal FW) that will do your heavy lifting with traffic management. You'd point to these Virtual Servers from your "proxy" BigIP. While you'd need another pair, it would give you the maximum flexibility.
It sounds like the goal may be to collapse a farm of reverse proxies into a BigIP pair, correct? This sounds like a perfectly valid use case to me.
-Matt
Nimbostratus