Two comments about this.
1. This method of determining a UUID is not time persistent. If the same problem and geogebra applet are run again the UUID will change. I don't know whether this would cause problems. It's something I tried to avoid in labeling images, including on the fly graphics. In the case that these items are cached you could end up with multiple copies that differ only in the label. For graphs this was not always a good idea.
2. I think you should extend alias() to refer to the geogebra applet. Alias() is designed to reduce the load on the problem writer from remembering exactly where the auxiliary file is located, but it also records the auxiliary file path so that eventually we can automatically include all auxiliary files associated with the pg file. (In this case it might be a link to a geogebra applet in the cloud.)
I've been trying to reproduce what I see in the ActiveCalculus example. So far I haven't been able to get the same effect from tests of different graphs in HTML pages. Can you send me a sample of the PTX that produces that page?