Just testing with the standard debian Virtual applicance and 2 pve's, and online migration failed.
/usr/bin/ssh -t -t -n -o BatchMode=yes 192.168.1.245 /usr/sbin/vzmigrate --online 192.168.1.244 101
tcgetattr: Inappropriate ioctl for device
OPT:--online
OPT:192.168.1.244
Starting online migration of CT 101 to 192.168.1.244
Preparing remote node
Initializing remote quota
Syncing private
Live migrating container...
Error: Failed to suspend container
Connection to 192.168.1.245 closed.
VM 101 migration failed -
/usr/bin/ssh -t -t -n -o BatchMode=yes 192.168.1.245 /usr/sbin/vzmigrate --online 192.168.1.244 101
tcgetattr: Inappropriate ioctl for device
OPT:--online
OPT:192.168.1.244
Starting online migration of CT 101 to 192.168.1.244
Preparing remote node
Initializing remote quota
Syncing private
Live migrating container...
Error: Failed to suspend container
Connection to 192.168.1.245 closed.
VM 101 migration failed -