Mike,
Will the AVB and Cobranet VLANs ever share the same port in the network? When AVB is enabled, AVB traffic is prioritized over all other traffic, so if the two technologies share a port there is the possibility that AVB traffic could cause sync issues on the Cobranet network.
If the two networks never share the same physical ports, I believe it should work. The only concern would be making sure that Cobranet traffic does not overwhelm the switch CPU for some reason and interfere with AVB control traffic.