Sorry, i don’t own a Synology NAS or Stream … but here’s my 2 cents regarding DVD’s
1) Rip your DVD’s to *.ISO … less hassle, easier to manage, less problems. but a *catch* you have to use Network Shares (*iso isnt widely (or at all) supported for Media Shares … aka UPnP / DLNA)
- Resume points for Dvd playback create a *.BMK (or “Bookmark”) file next to your media … i know it does it for Local USB Hard drives and the Internal HDD … unsure whether this *bmk gets created via Network Shares (i would’nt recommend using Media Shares at all)
finally if you decide you want to keep using VIDEO_TS folders … here’s a little renaming *trick* that works (contrary to what the user manual states) 
Give it a try, … also press the “Play” button on a folder (not the “OK” button) it will then play all the folders contents in sequentual order.
http://community.wd.com/t5/WD-TV-Live-Streaming/DVD-folder-thumbnails/td-p/648697
