I was wondering if it is possible to include SVG content inside a panel (or whatever would work in GWT), be able to add more to the SVG (like add a circle or a curve) programmat
Be warned that SVG will not work in current GWT Shell (Hosted mode) up to 1.6 inclusive, because:
1) on windows, it uses IE component
2) on Linux, it uses Firefox 1.0 or equal mozilla runtime, which has no support for SVG.
Compiled code works fine in non-IE browsers.
Also, it works regardless of HTML/XHTML in browsers, because in GWT you use createElementNS (you can code method yourself using JSNI). Also, your SVG tag may need width/height attributes (see SVG spec).