You may be OK. It is an older device and may not ever get tested or approved. The HBAs and the Hosts will be the important things to get from the supported list. Are you currently using it with 3.5?
Yes. I'm currently running 3.5u3 on p2950s. But we are planning on installing Dell R710s with the latest and greatest. The HBAs are on the HCL for ESX4 in the R710s. It just was a list minute notice the CX700 wasn't. We are migrating to a CX4 later on in 2010 but was wanting to adopt vSphere before hand.
Since you are going to be fully testing this anyway you will be able to post back your experiences setting up and running vSphere 4 on a CX700. How great is that.
I am in a similar situation. We have cx700 still in use by our 3.5 ESX servers. We are migrating production LUNS to a new CX4-480, but I really would like to continue to use the cx700 for dev/test as long as it has life. Our migration to vsphere is imminent in 4-8 weeks.
I found the following article on vmware's website, in which they are testing thin provisioning performance. In this particular study, they used vSphere 4.0 build 164009, an EMC Clariion cx700, and 16 proliant DL380 servers. Since they were testing disk performance, I think it can safely be assumed that the cx700 functioned correctly, or their results would have been meaningless.
So even if it is not listed in vmware's supported matrix, vmware used a cx700 successfully in a vsphere environment. I will still test before I implement, but I am expecting no issues.