The company at which I work has two small 5.5kva generators we were hoping to be able to use both of them in case of emergency. The idea would be to power two different circuits through the circuit breaker box with the high side separate but the neutral returns common to both. Is there any inherent risk to the generators with this approach?

Assuming you will be using a transfer switch of some sort with a solid neutral,(not switched), all the neutrals will be common, to include the system neutral and the neutrals from both gensets. This will not cause any harm to the generators.

Assuming you will be using a transfer switch of some sort with a solid neutral,(not switched), all the neutrals will be common, to include the system neutral and the neutrals from both gensets. This will not cause any harm to the generators.
Thanks for your help