Well my watch says yes. The heart rate certainly rises more than sedentary, and usually attains the moderate range on a fitbit or whatever.

I've experimented a bit with this. If you really want to get the heart rate up, you can move to a relatively low gear and do the spin fast and glide thing. But even just riding normally, there is a significant effect. It may feel like the motor is doing all the work, but you're likely pushing more than you think.

I guess if you're talking muscle-building, you could shut off the motor for a stretch? E-bikes are heavy and you will get a good workout in that mode, though the fun level may drop. I do this sometimes on a trail with lots of Pokemon Go stuff. I go to the lowest gear and ride really slow with no motor to hatch those damn eggs already! :p