Any overnight train from Tokyo to Hokkaido?

If there aren't, are there any trains from Tokyo to Hokkaido?
Are they covered by the JR Pass?
How long is the journey from Tokyo-Hokkaido and Vice Versa.

No, not anymore, unfortunately.

If there aren't, are there any trains from Tokyo to Hokkaido?

Though there are no "night trains", Shinkansen runs from Tokyo to Shin-Hakodate-Hokuto near Hakodate, in Hokkaido

https://world.jorudan.co.jp/mln/en/japan-rail-pass/?p=0&xpd=1&from=Tok...

and as the result shows, this train is covered by Japan Rail Pass and JR East South Hokkaido Rail Pass.

http://jreasthokkaido.com/easthokkaido/e/

How long is the journey from Tokyo-Hokkaido and Vice Versa.

Hokkaido is a big island, depending where your destination is, could be 4, 5 , 6 , 8 to more than 10 hours from Tokyo.
http://www.hyperdia.com/cgi/en/search.html?dep_node=TOKYO&arv_node=SAP...

iHow long is the journey from Tokyo-Hokkaido and Vice Versa.

Hokkaido is a big island, depending where your destination is, could be 4, 5 , 6 , 8 to more than 10 hours from Tokyo.
http://www.hyperdia.com/cgi/en/search.html?dep_node=TOKYO&arv_node=SAP...

Tokyo to Hakkaido by shinkansen is basically four hours (Hakodate-Hokuto). From there is it another four hours to Sapporo. And, yes it is covered by the JR pass. Other locations around Hokkaido - from less than an hour to many many hours. A lot of people fly.

The night train (Cassiopeia) was removed from service when the shinkansen was extended to Hokkaido (ended March 2016). It was a difficult to book service, and actually quite expensive when I looked into it a few years back. The JR pass did not cover the room cost (from 27,000 yen for the most basic), only the base fare.