Theoretically yes, but practically no.
Because it will require lots of works to take apart the template overriding only from the DarkMart You may try it, but it will give you lots of pain. Especially with the CSS. Because what ever comes with the CoolMart are meant to work all together.
This is why we have:
- CleanMArt
- PureMart
- FashionMart
Those 3 templates are only VM2 Template and they were designed to be integrated into any 3rd party joomla template, and stylize the Virtumart related pages only.
Regards.