Hi F5fanboy,
a.) Yes its supported. But you may have to use certain SNAT configuration on the F5, to make the request and response pass your LTM.
b.) In a clustered scenario LTM needs at least 3 IPs (2 self and one float) for every route domain. But you don't need Interfaces/IPs in any of your VLANs, if a different network path could be used to reach the LTM. To have LTM receiving the traffic for non-local connected networks, just may want to use directhost/32 routes on your network equipment pointing to an LTM interface of another VLAN.
Cheers, Kai