Director itself doesn't care whether the AMI uses HVM or PV, but EC2 instance types are often only compatible with a single virtualization type. As you say, Amazon recommends HVM for the R3 instance type.

Here's a pretty good blog post on virtualization types:

http://cloudacademy.com/blog/aws-ami-hvm-vs-pv-paravirtual-amazon/

That describe-images command is just an example, and you can change the parameters to suit the particular AMI details you are looking for.