OpenVZ is definitely not Vserver-based.
Moreover, Virtuozzo/OpenVZ historically precedes vserver:
Virtuozzo/OpenVZ was started in 1999, first sources were made public in 2000 and the production version (1.0) was released in 2001. AFAIK, vserver project started only in 2001.
Vserver and OpenVZ code is very different.
The similarities exist only in the ideas and approaches, because they both provide virtualization. However, if the similarities have other reasons than the same task of these two projects, the ideas probably migrated in the opposite direction than what you imply, from OpenVZ to vserver. But I'm not certain if it really took place.
