I am running it fine on a MacBOOKPro, but a MacPro should be similar as long as it is a fairly up to date system. Intel-VT needs to be enabled in the BIOS. Make sure you have the latest BIOS updates installed as well.
How to check that Intel VT-x is supported in CPU:
1. Open Terminal application from Application/Utilities
2. Copy/paste command bellow
sysctl -a | grep machdep.cpu.features
3. You may see output similar to the one bellow
Mac:~ user$ sysctl -a | grep machdep.cpu.features
kern.exec: unknown type returned
machdep.cpu.features: FPU VME DE PSE TSC MSR PAE MCE CX8 APIC SEP MTRR PGE MCA CMOV PAT CLFSH DS ACPI MMX FXSR SSE SSE2 SS HTT TM SSE3 MON VMX EST TM2 TPR PDCM
If you see VMX entry then CPU supports Intel VT-x feature, but it still may be disabled.
Check out this as well:
http://kb.vmware.com/kb/2009580
Running 64-bit VMs
If your processor is an i3 or greater (that is, you do not have a Core 2 Duo) you can enable nested VT. This allows you to run 64-bit virtual machines within ESXi. To enable nested VT, add this line to your .vmx file:
vhv.enable = "TRUE"