No, it is not possible to host either Xen PV, Xen HVM or KVM VPS on your SolusVM Master regardless of which License you choose.
To increase the number of slaves to your license please login to your Client Area, click on My Services and select your license by clicking on the small icon to the right, then click Upgrade / Downgrade Package. From there you will then be able to enter the number of slaves you wish to change your license to.
We currently support OpenVZ, KVM, Xen PV (ParaVirtualization) and Xen HVM (Hardware-Assisted Virtualized Machine). You do not need a different license to use any of the supported Virtualization Types, all Licenses support all types!
Your SolusVM Master can be installed onto a VPS and is infact something we recommend as taking backups from a VPS is alot easier and quicker to restore than a Dedicated Server, you will require the Slave Only Master License in this enviroment as you cannot host VPS on the Master when it resides on a VPS itself.