I did once build an olive in VMware and can confirm it works. However just to tell you upfront, there were a lot of issues with multicast over the vmware interfaces. This would mess up things like OSPF etc. Best is to build an olive om some old machines with intel nics...
Can't give you a VM unfortunatly because i can't provide you with the juniper software and i don't think i still have it on my pc...
Dennis