Please TELNET into the DS and try the following (But we don't promise it will work in the new DSM3.0 this time, please kindly keep us updated if it can or can not work this time, it is quite important information to us).
According to compatibility list: http://www.networkupstools.org/compat/stable.html
The APC Smart UPS is not supported by usbhid-ups driver.
However, it maybe supported with some trick.
1) If you see the /var/log/messages fulled with "Can't connect to UPS. Try to re-start driver" and run "ps | grep ups" see it stats upsd but not usbhid-ups
2) You can try to run "upsdrvctl start" and you may see the following messages: (Using APC SmartUPS 750 for example)
This APC device (051d:0003) is not (or perhaps not yet) supported
by usbhid-ups. Please make sure you have an up-to-date version of NUT. If
this does not fix the problem, try running the driver with the
'-x productid=0003' option. ...
3) Edit /usr/syno/etc/ups/ups.conf, append a productid line to the [ups] section as following.
driver = usbhid-ups
port = auto
productid = 0003
4) Try to run "upsdrvctl start" again, and it should work!
If it does not work then the UPS is having compatible issue with the DS, and it can not be supported.