What's my greatest risk without the interface - the BMS detects a failure mode and can't tell inverter to shut down?
If the overkill decides there is a failure (such as low voltage), it will turn off all power to the inverter and the inverter will shut down... so in a rather abrupt way, the inverter *is* signaling the inverter by shutting off power. This is a tried and true way of operating...... as long as the BMS is rated for the currents involved. One cautionary note: I don't recall the brand, but one brand of solar chargers specificly says that if they are shut off from the battery it can damage the SCC. I would avoid any such charger.
What pushes me to more sophisticated signalling between the BMS and the Inverter is when the current gets higher than the available BMSs can handle. Your described situation is right on the cusp of that, but the Overkill should still be OK. If you needed 110A.....I would be advising differently.
One way people work around the current limit on FET based BMSs is to have multiple batteries in parallel. In your case, it would be two banks of 16 cells, each with it's own overkill BMS.... then the total current from the two batteries would be 200A.
The next option is to use signals from the BMS to turn contactors or SSRs on-off to control the current. This is essentially the same model as the FET based BMS like overkill but the FETS are external to the BMS. To tell the truth, I have never done this. If I am in this situation I go to the next option.
One step more sophisticated is to use the signals from the BMS to turn the inverters and loads on&off rather than try to turn the current on&off. However, to do this there has to be a way of controlling the inverters, chargers, and loads. The best brand of inverters and chargers for this type of set-up is Victron (particularly for inverter-chargers). However, there are other brands that can be made to work.
The final level of sophistication is when the BMS tells the loads & Chargers to turn on/off via a network of some type. There are a few BMSs that have developed the necissary protocols to talk with some specific equipment, but if they don't specificly say they can talk to the equipment you want, assume it can't even if it has the same network interface (like CANBus) Currently the industry is pretty fragmented so there is no standard. That means the choices of what can work with what is pretty limited. Maybe in the future there will be standards that make this a lot easier to 'plug and play'
Would it be fare to say the Inverter is controls overall (bank) charge rate while BMS controls individual (cell) charge rate?
I am not sure I would say charge rate.... I would probably say the Inverter controls the battery charge voltage and the BMS does not let the charge voltage for either the battery or the cells get out of bounds.
Charge rate is more or less an accumulation of what all the chargers are pumping into the battery. Many BMSs can monitor this and shut off charging if it gets too high.