Is there any know issues with running 2 instances of SuiteCRM (on different servers), both instances pointing to the same database?
Could be have some problems. SuiteCRM work not only with database but also with files, from filesystem, for documents, for vardef and personalization of view and field definitions, etc, etc.
For example if you add a field or you change a view in one instance, the other can produce some errors.
You should syncronise the files of the filesystem to make it work correctly.
Apart from what Roberto already said, I wonder what exactly you are trying to achieve? Are you just worried about performance, because you have a big installation with many users?
Because there are ways to scale the architecture, but they are not necessarily the one you’re asking about.
Typically, putting a load-balancer before the multiple SuiteCRM servers (but keeping these as exact replicas), with a single database at the back end.
Or using some similar scheme to scale the database to more than one server (but in a way that SuiteCRM sees only a single database, and all replication and data consistency processes happen behind the scenes).