In general, you can have multiple databases hosted on single database instance. It is not recommended to create or alter any schema's or table in AF database but you can create separate database for PME in the same instance where SRVAF(database) is hosted. Also recommend to allocate system resources as per system recommendations for AF database to perform normal.
This isn't a problem, but as Lal suggested, be very mindful of resources and performance. The SQL Server should meet the minimum requirements for PI AF, as well as have any additional resources required to the well functioning of this other database/application. If PME requires a lot of resources on the SQL Server, unless you have a small PI AF System and don't plan to scale, I wouldn't put the DB on the same SQL Server.
Are you currently using Asset Analytics? Where is it located?