Are the 2 RJ45 GbE connections are isolated circuit paths? 

Yes, Both RJ 45 ports are separate/isolated. 

IS the throughput / data rate 1Gbs combined or per RJ45 port?

The throughput/data rate is 1Gbit/s per Port, as a 10Gbit/s backbone works in the switch.

Does the device offer VLANs, IEE 802.1, IEE 802.1Q ?

The core of the OET 1510/40 is basically a managed switch, so a lot of features are possible. Port 1 is configurable via port management tools and it support VLANs and the latest  IEEE 802.1 Audio Video Bridging Standards. The Switch supports IEE 802.Q aswell , If the customer has tagged IP-packets they will be transferred without any additional configuration.