I just looked at their website more closely and it looks like CR Magnetics also has a normally closed current switch, I didn’t even see that when I looked earlier. If this works like I think it should, use a CR9480 with an NPN transistor output wired to an RE201 and it should work as one would expect (not backwards like a CR9380 would have). The sensor/zone would normally be closed and it would open when the sump pump runs, with each opening and closing being logged in the Alarm.com event history. You would be able to program Alarm.com notifications for when the sump pump turns on.
http://www.crmagnetics.com/Products/CR-9480-P163.aspx
http://www.crmagnetics.com/Products/Assets/ProductPDFs/CR9480%20Series.pdf
Sorry for the confusion, I just learned about CR Magnetics this morning and I wasn’t aware of their full product line. The exact part numbers on their site would be CR9480-NPN or CR9480-NPN-M, either should work.