yes, you can use HTML in product descriptions. just click on the 'view source' button to enter HTML code directly if you want.
The point here is that many tags are being immediately blocked.
As example:
<iframe> does not work. It appears as text.
If there is anything related to java scripts is immediately being blocked.
So in such a case I can not use typical HTML but somehow restricted version.
What to do to have a possibility to use full html without a risk of editing tags by the JEM?