I moved you thread in correct forum.
did you running the correct VTM Licensed Version ?
No experience as such, but it would appear that "Proxy Protocol" is simply a more informative header than x-forwarded-for that the vTM adds by default.
Can you explain what it is you are looking for here? You could use a TrafficScript rule to add the header if you need it, or use the x-forwarded header if it contains the information you need for the back ends.
Could you please let us how you chain your LBs?
Is it "ELB -> vtm" or "vtm => ELB" ?