I had not previously seen Carlton Doe's excellent article on Informix licensing. It can be found here.
A tip of the hat to Claus Samuelson for bringing it to my attention.
IBM License Metric Tool is a no-charge offering that helps calculate number of Processor Value Units (PVUs) including supported virtualized servers that are available to installed Passport Advantage PVU-based software.
This is not just another product, it is free technology that aids in the compliance and remediation space that we all struggle with. (Well, not me personally, obviously! :-) )
Since people will inevitably ask for help with this no charge option, there is some free education available on the 12th of August. This will equip you to commission this technology for yourself.