I too have tried in the past to get the widget to work in Mountain Lion... with no success. Until today!
No idea what exactly has changed, or where, but after loading the widget in one more "futile" attempt I set the account credentials and hostname (and the all-important "remote" checkbox) on the widget's reverse side. Low and behold I saw my Devices! And Actions! And Variables!
And the crowd goes wild.
In case it matters, my current systems involved in this test are a laptop running 10.8.5 that has the widget and my 10.5.8 Indigo server system running Indigo Pro 5.1.6.
Perhaps others will also find the widget working for them that had previously given up on it. I am certainly glad that I tried it one more time!