Yes, you can turn off the Activity History items if you rely on Interesting Moments. They are not linked in any way.
Usually I recommend keeping 2-3 Activity Histories on because it can help with historical data if you leave Marketo or if MSI doesn't work for some reason. Sales people may linger on Activities if you've trained them to do this. Of course, if you turn it all off, they'll be forced to use MSI.