You would use one HANA DB, with multiple schemas. You will migrate all your MSSQL databases onto one HANA DB. This is the supported and most cost-effective way to do it - assuming all your MSSQL databases will fit.
Otherwise as Sunny says, you will need multiple HANA DBs in production, which currently means multiple servers. This advice is likely to change soon in relation to VMWare, but not until quite a lot later in relation to multiple DBs on one virtual machine, in production.
John