I am not aware that Muntjac will actually harass Roe to the extent that the Roe will leave the area.
Neither do they appear to compete seriously for food; at least as long as there is plenty around.
However, I seem to remember reading some years ago that there appeared to be evidence that Roe disliked too dense a population of Muntjac and would try to migrate out of the area and that, of course, could cause territorial problems elsewhere.
If you have concerns about Muntjac numbers, the solution is to shoot as many as possible.
They are good eating and come in a handy, portable package which makes them easy to carry out of the woods. I find this more attractive as I get older!