Usually there are no problems using Nalu with different widget libs. GWT, GXT, Elemento, Element and Domino-UI are working well with Nalu. There is one thing you need to check: Is you ui-lib widget based or element based. Then choose the right module and everything is fine. In case that there are 'very special' SmartGWT implementations, we can think about creating an own SmartGWT-Model.
I am not familiar with SmartGWT. But as long as all SmartGWT-code stays inside the component, everything is fine.