VM2.0.26a > VM2.0.26b > VM2.0.26c > VM2.0.26d
There is absolutely no difference between those sub-released (in terms of compatibility between our templates). Beside, those letters sub-releases are very minor updates. If i were you guys, i would just skip all sub releases - UNLESS THEY ARE FOR SECURITY.
But, yes; PureMart supports VM2.0.26d, just like how it supports VM2.0.26 or VM2.0.26a
Regards,
Support