You can use a generic system user (e.g. BOBJUSER) but all actual BOBJ users will "inherit" the roles/privileges of this BOBJUSER created in the HANA database. You can do this when you create the JDBC connection between BOBJ and HANA.
It is analogous to BW/HANA where there's one user connecting the BW application to HANA DB but application level security is handles in BW and not in HANA.
So you would need to structure your user-specific security in BOBJ. Obviously HANA Analytic privileges can't be used either with one HANA id.