When I converted my Sessions Collections from UPD to FSLogix. I ran a script that effectively copied the UPD vhd's to new FSLogix vhd's. This was too keep user settings etc. But in the end UPD is disabled and we we only use FSLogix. If you are using full FSLogix Profile, you don't need the old UPD and you don't need it enabled.
But to answer your question, do you need to disable UPD apparently not, but you probably should.