The system may or may not need to be grounded. The battery itself is a source. Code may allow grounding when required to be at a point other than the source. Generators are not always grounded at the generator. Separately derived systems are not always grounded at the separate source either. If this system is required to be grounded it possibly can be done at the inverter.I don't know what that has to do with whether equipment grounding is required by code.
Just bonding the battery case? Why would that be no different than needing a SSBJ back to a transformer case if the system bond is at the first disconnecting means? Unless maybe there is some code section that doesn't require case to be bonded at all - that I'm not certain about yet.The case.