That is true that electrification stops in Dover.
However, NJT considers everything past Dover to be part of the Boonton line, not part of the M&E. I'm not quite sure why they do that, or if they even still do that, but at one time the M&E schedule didn't even bother to list the stops past Dover. You could only find the schedule for those stations on Boonton time table and in fact it was only Boonton line trains at one time that ran past Dover. Now there is a mix, with some running the M&E and some running the Boonton line.
So based upon that, the M&E is fully electrified.
The official M&E timetable shows timings of trains all the way to Hackettstown. Generally the colored NJT maps show both M&E and Montclair-Boonton extending to Hackettstown. See for exampe:
http://www.njtransit.com/pdf/rail/Rail_System_Map.pdf
Generally trains to Lake Hopatcong/Mt. Olive/Hackettstown numbered 1xxx go via Montclair-Boonton and 8xx via M&E.
Now to the basic question. The following NJT lines are electrified:
1. North East Corridor, NY Penn to Trenton and then to Morrisville PA yard 11kV, 25Hz.
2. North Jersey Coast Line,
New York Penn to just past Matawan (Lloyd) 11kV, 25Hz.
from (Lloyd) to Long Branch 25kV, 60Hz.
3. Morris and Essex, Hoboken to Dover, 25kV, 60Hz.
4. Gladstone Branch, Summit to Gladstone, 25kV, 60Hz.
5. Montclair - Boonton, Hoboken to Great Notch, 25kV, 60Hz.
and incidentally Denville - Dover, 25kV, 60Hz as part of M&E.
6. Newark City Subway and Newark Light Rail, 600v(?) DC.
7. Hudson Bergen Light Rail, 600v(?) DC.
I am not sure about the exact voltage of the DC electrification for the LRT lines.