Are there Portlets in Volto?

tl;d: Not yet.

Since Volto relies/depends on the RESTAPI and the RESTAPI has not (yet) any entry points for portlets the answer is no.

See the comments under the following topic:

There you'll find a link to a branch that exposed portlets to the RESTAPI. But it seems abandoned b/c of lack of enough interest in the Volto world for portlets. (See comments in the mentioned topic)