if you means: grab the whole MESS tree, you're wrong most of the times (unfortunately, these days you would be right due to the malloc changes)
replace 'these days' with 'quite often' and you'd be right. Significant changes are seem to be being made more often than not. As soon as I dump MESS in a MAME tree it means I can no longer update that MAME tree from SVN due to the chances of everything breaking.
This has been the case the last 5 or 6 times I've decided to take another look at MESS. Call me unlucky with my timing, but that's what I've found.