It is my understanding that Synology treats the DS212 (88f6282) as it does the 88f6281 CPU. They refer to them both as 88f628x and only provide a single toolchain. You should be able to use the 88f6281 package posted.
http://pkgs.marktompkins.me/packages/urbackup-server_88f6281-5.1_1.4.8-1.spk
I see, thx, I’ll try that 
Hm, I don’t know, I just tried it. Installation went without errors it seems and the package center says the server is running. However, when opening the Webinterface (on port 55414, via LAN) nothing happens. The browser states it’s connected, but it endlessly stays at “Connecting…”.
Removed the link to this thread from the download page now.