<ul>
<li>Element</li>
<ul>
<li>Subelement...</li>
You can pretty freely use HTML inside javadoc comments.
Update: Because it came up, I tried
<ul>
<li>one</li>
<ul>
<li>one point one</li>
</ul>
</ul>
and get
- one
- one point one
I agree proper nesting is better.