what kind of database server are you using - oracle or sqlserver ?
for oracle bsa and bdssa (and bdssa_portal) must all be in separate instances if they are on the same system.
for sqlserver that's not an issue.
the reason for separating them on different database services is performance. if you plan to have a high usage site for bsa and bdssa you need to have a database server that can handle whatever load you are throwing at it. running lots of jobs and running an ETL all at the same time is very resource intensive. so that can work fine on a single database server given the right hardware or you might need separate systems.