I'm having a similar issue with DSM 5.1.5021 update 2.
Try connecting over finder with ctrl+K and then entering the fully qualified path, e.g : afp://192.168.x.x/ - that should work.
Try adding the user to the "system default admin group" and then see if - when trying to connect through finder - the shares for that user show up.
I have another box running dsm 4.3 which does not seem to suffer from this issue ( also non-admin users can view the shared-folders available to them ).
My "solution" is to add admin-rights for every user ( not that I like it, but I don't have a better solution and the box is only used privately / non-commercial ).