But Tinyportal do use the native theme - the default one. That'is the one that gets "modded" when you install the mod....
As for making ALL themes automatically work, it can't be done..because the clever theme system of SMF ( that allows it to look like anything) first search for your chosen theme's files, (index.template.php MUST be there), then if they are missing, look for the same files in default folder.
So, if you just change a few things (from the default), you may only have to include 2-3 template files. The rest is fetched from default folder.
The reason its difficult to change whatever theme you have in its because no theme is alike, codewise. And the mod searches for blocks of code that may or not exist in this new theme.
So, the only way is to modify by hand , these new themes. But on the other hand, its just ONE file that needs tweaking. I don't want to exchange the freedom of writing such different themes as Helios and Simplicity for a more universal system that don't allow more than some graphics and color change. The developers certianly don't want it either, its one of the things that set SMF apart from others.
There is also a lot discussions around this on the SMF site.