User Provisioning Service and Indentity v4 are an API version of the employee flatfile. So clients should do one or the other. Only in rare circumstances should you do both.
UPS, at this time, will allow you to do all record types < 600 which should handle most clients. It does support, in a way, the 750, 760 record types but its implementation is different. It does not currently support 700/710/720 record types. For clients needing 7xx records, they can implement UPS and still use the employee import for those 7xx records. I would not recommend using UPS as well as employee import for 3xx records unless you can guarantee no overlap in the data (i.e. 2 HR systems, etc). Based on my experience, I have never seen a company with 2 HR systems with 0 overlap. There is usually managers that approve employees in both HR systems and therefor exist twice.
