Can I have two gateways using the same SQL database for historic logging?

Question’s in the title. Is this possible / recommended?

I have a front and backend split gateway, but I want to trend some system tags on both systems and really I don’t see the need or want to have two databases, one for each, so I wanted to create a database connection on both pointing to the same SQL instance and database. I’m not sure what chaos this will create though (if any) and also how partitioning will be affected?

Not a problem at all (as long as they have distinct gateway names).

The historian already uniquely identifies every record by what system and tag provider it came from.
Check sqlth_drv, there will be at least two records (one null, one probably with an entry for default) for each gateway you connect to a given historian.