Chiming in late, sorry.
The short answer is: no, as you pointed out uDig doesn't support google tiles because it is not permitted by license. I know QGIS is doing it but I am quite sure they shouldn't.
At least that position a few years back when we wanted to add it to uDig.
We discussed it quite some time in the community and funny enough several of us had code to download the tiles. But the end verdict was that it would not be possible.
Just for info, back then, with the prototype code that was used to simulate such a google tiles downloader, the thing worked a few minutes, then the service was blocked from serverside.
I guess it could be used in case one has a commercial key, but I am not sure about it.
In case one would find out it is legal and accessible, uDig now has a tile mapping service support and it would be quite simple to add a custom tiles downloader, the same way it is supported for Openstreetmap layers for example.
(see http://jgrasstechtips.blogspot.it/2012/05/udig-web-map-tiles-enhancements.html )
The plugin that handles all this is located here: https://github.com/uDig/udig-platform/tree/master/plugins/net.refractions.udig.catalog.wmt
I would anyways suggest to discuss an approach in the uDig mailinglist.