Yes, SI short for Sunny Island, SB short for Sunny Boy.
I didn't know smart meters had a contactor; is that to disconnect non-paying customers without human contact?
If you have a transfer switch, make sure inverter (SB or SI) sees 5 seconds "off" time before reconnecting to a different out of phase source.
SMA warns that SB must be prevented from backfeeding generator. SI can provide that function.
If your generator increased enough in frequency, would accomplish same. But need to be sure it provides sufficient protection.
If you've got current transformer (and voltage monitoring) for power flow, can probably do pretty good job of it. I'm interested in that for limiting backfeed, e.g. if I have more PV watts available from SB that can be backfed through SI, or than utility agreement allows.
You might be able to reach about 100% from PV, with generator just providing voltage/frequency source, if frequency stays within range.
The on-grid UL-1741 or UL-1741-SA limits are tighter, while off-grid allows much wider voltage and frequency.
A dump load could be another way to deal with excess PV. SMA used to sell a smart load, basically a Sunny Boy working backwards putting variable DC power into a load like resistance heater. A dimmer would be a crude way, maybe too poor a power factor. Motorized variac could do it, but has to be big. Switch-mode power supply with good power factor correction would be another.
Sunny Island (or other AC coupled battery inverter) might make a nicer system for you, only running generator when needed. Batteries would buffer the PV system most of the time.