I tested successfully the former solution during 2 weeks, making openvz to work on a 64 bit x86_64 CPU.
This allows my system to use vzpkgcache, vzyum and vzrpm without any issue.
The "side effects" I feared to found were not very harmful. I only have to report those two:
1 - We can not use the prebuild cache template tarballs downloaded from openvz website. Only the cache templates created with vzpkgcache works correctly with vzyum and vzrpm.
2 - yum-cache directory is not a common directory for all VE's. Each VE has their own yum-cache directory.