HA cluster is absolutely independent on CPU architecture, so you can even mix Xeons and Opterons. However it's a good practice not to make such mixes.
---
VMware vExpert '2009
http://blog.vadmin.ru
EMCCAe, HPE ASE, MCITP: SA+VA, VCP 3/4/5, VMware vExpert XO (14 stars)
VMUG Russia Leader
http://t.me/beerpanda