Let\'s say I have peering set up as follows: A<->B<->C and want to route traffic between vnet A and C
Is this currently possible? Perhaps a vnet gateway in B &
For now, it is not possible.
VNet peering is between two virtual networks, and there is no derived transitive relationship. If virtual network A is peered with virtual network B, and if virtual network B is peered with virtual network C, it does not translate to virtual network A being peered with virtual network C. UDR could not achieve your scenario.
Why not set up as follows: A <->B B<->C A<->C?
More information about Peering please refer to this article.