Yeap!
The module "_rpmmodule.so" seems to be 32 bits and not 64.
It seems that's better forget vzyum and vzpkg by now and try alternatives.
The only one I know until now is to use yum inside VE, but as you said, it consumes a lot of memory and breaks with default configuration file.
I had to change some variables in /etc/vz/conf/<VEID>.conf to have a yum update inside a VE without errors.
AVNUMPROC="200:200"
NUMPROC="400:400"
NUMTCPSOCK="500:500"
NUMOTHERSOCK="500:500"
then run "vzcfgvalidate" to check configuration file.