GateIn support almost common features of Google gadgets such as dynamic-height, settitle, userpref, mimimessage, etc. you can test with the samples here: http://code.google.com/apis/gadgets/docs/ui.html#Dyn_Height
But I don't purely sure all run good, so please report issue (https://issues.jboss.org/browse/GTNPORTAL) if you find problem of any feature gadget.
I just re-test dynamic-height and settitle from sample link above. They run good on GateIn 3.1
Yes, GateIn 3.1 supports all of Google Gadgets API, just not when running in HTTPS or secure mode. I have editied a js file inside a war file to fix the issue. This is probably fixed in GateIn 3.2. At least I hope it is.