Are you reviewing current stats (i.e. refreshes every 20 seconds) or reviewing a specific timeframe for the stats and getting "0" value data?
I would check vpxd.log in vCenter for possible indications of problems. The hypervisor should be able to collect VM CPU utilization stats regardless of VMware Tools because the the vCPU is assigned directly to the physical CPUs by the scheduler.
Also what are your statistic intervals, save durection, and levels set to in vCenter?