It's really going to depend on your virtualization software and how well it can 'hide' the underlying hardware from the software.
Generally speaking you should have no problems running any of the ASE versions on a virtual machine. The $20K question of course is whether or not your VM can hide the physical level from the Sybase SYSAM licensing software! ;-)
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I run VMWare at home. Host is a quad-core. My guest systems are configured with 1 processor and 1 or 2 cores per processor, for total cores of 1 or 2 per guest.
The SYSAM/cpuinfo script (running on the guests) only recognizes the 1 or 2 cores allocated to the guest; SYSAM/cpuinfo can't see the 4 cores at the host level.
I'm running a mix of ASE Enterprise and Developer Editions, with the Enterprise servers reading from local SYSAM license files, with a couple different license types (eg, SR and CP). For the CP licensed VMs the dataservers will check out only enough licenses to match the 1 or 2 cores allocated to the guest.
I'm not running Sybase sub-capacity licensing on any of my VM guests.
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At a recent client we were running all of our Sybase servers on AIX/LPARs
The physical hardware for the application group I supported consisted of 2 physical frames, each with 8 quad-core chips (total of 32 cores). (Or was it 4x 8-core chips? *shrug* ... regardless ... total was 32 cores per frame.)
Our Sybase-related LPARs were configured in such a way that the Sybase software (ASE 15.5, RS 15.6) only saw the cpus assigned to the LPAR. We were running with straight CP licenses (ie, no sub-capacity licenses in use).
During DR testing we did have a problem where the AIX admin had misconfigured the LPAR with the net result being that the ASE instance could see all 32 cores at the frame level even though the LPAR was configured to use only 8 cores. Needless to say (?) we couldn't get ASE to startup with *only* 8 cpu licenses; and yes, we had the admin reconfigure the LPAR to make sure ASE only saw 8 cores.
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At my current client they're migrating everything from HP to AIX/LPARs. For whatever reason the client has opted to run the ASE/RS instances with sub-capacity licenses ... even though SYSAM/cpuinfo can only see the cores assigned to the LPAR ... go figure ...
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NOTE: While I've worked on a few VM systems I am by no means a VM 'guru' ... I basically use what's given to me (eg, at clients) or I flip a few switches (at home) until I get what I want! ;-)