Hi Googlebug,
The Synology DS series didn't read external HFS+ drives a couple of years ago, so I'd guess they still don't. Some people hacked in HFS+ support (I was one of them) but it wasn't a fun experience.
Edit: Well hey,
these guys reckon you're good to go for read only since DSM 4.2 and higher support HFS+, but you need to
disable journaling for read/write (it's from 2013, so maybe the situation has improved further:
not as of 2014). Maybe I should have kept mine :-) I'll stop here because I've gone from personal knowledge to Google-foo.