Resource pools are designed to segment/reserve physical resources for groups of vm's and not really for use as a logical separation within a virtual infrastructure.
One simple way to make the logical separation would be implementing a naming convention in you inventory. Simply prefixing the name in VI with something like validation_<servername> then sorting the servers by name would create a logical grouping.
I'm always careful when there is the potential of depriving production vms of resources they might need within the cloud.
On the other hand changing the values within a resource pool is pretty simple and can be done when needed. So grouping with resource pools for logical reasons could be a workable solution.
A lot depends on how much utilization is happening in the production environment. If there are plenty of resources then the potential for harm from creating a resource pool for logical reasons is not much of an issue.
If you do use use a resource pool for the logical grouping I recommend making a note that the resource pool was created for logical reasons not for QOS reasons.
