This gets updated shortly after the new Mame goes live, there is currently no for the end user to know when it is updated but that is something on Jasons to-do list and even pick which version. Jason does update it the day of or the next day after the Mame release though.
This is if you use the Mame specific importer of course, this doesn't apply if you are using the normal import wizard.
I wish I could answer your question about the CHDs, I don't use them myself. I don't know what games are CHD files only, I was under the impression that they were companion files to go with the actual chipset dumps and as long as the path for them is in the mame.ini file it's fine.