I've been collecting legacy versions for a while, and haven't yet come up with a valid 3.x version.
Anyway, the 3.x and 4.x series are not compatible, they have very different install paths, support structures, different databases (Valentina vs. PostgreSQL) and the codebase/script APIs are different. There's also some differences in content formats.
Really, it wouldn't be of any use except if maybe you had some sort of plugin that you need to use, that only works on 3.x Daz.
You can run multiple copies of Daz concurrently though, no matter what versions they are.