I have my DAZStudio directories are pointed to my Poser runtimes and almost everything loads as far as props and figures. Now depending on the Materials used, some surface texturing and tweaking might be required to improve the quality of a render.
I’ve found a few items that don’t like DS4, but they’re older items (4+ years) and usually freebies—anything I’ve bought from the DAZ store still works fine. I’m using M4 and V4 far more than I use Genesis, and I’ve yet to find something for them that doesn’t work in DS4.
The only major problems with version compatibility are the other way round — Genesis stuff and anything supplied in the new D|S4 file formats will not work in D|S3 or earlier.
Note that some things are limited to D|S3, some plugins have updated versions which you’ll need to redownload and install, and some plugins were, unfortunately, never updated to D|S4. (Isn’t there a list somewhere of plugin update status?)