We have verified this scenario in development environment and it is possible to connect 2 different Farms to the same Nintex database. But we want to check if this is recommended in PROD movement.
I suggest you open a support ticket at Nintex or request help by a Nintex Partner. I expect community won't be able to give you much advice here. Nintex can tell you better what's recommended in the scenario you are going to run.
Thanks Enrico!!! our clients have already connected with support team and now we are being directed to Nintex product team but they are not able to response for last 2-3 weeks