Does breadmaker bread need to include milk powder?
A basic bread is 


flour
water
yeast or sourdough
(salt)


With these base ingredients, just by varying flour type, ratios and preparation method, you already get a wide range of breads, whether made by hand, kneaded in a mixer or dumped in a bread maker.

Extra ingredients influence the crumb texture and / or the taste of your bread. Including some fat, for example, makes the crumb "fluffier", using milk instead of or in addition to water gives finer pores and alters the taste a bit.

If all recipes that came with your bread maker include milk powder, I'd assume this to be a quirk of the author, not a necessity. I'd simply leave it out. You could add a teaspoon or so of vegan fat, but I don't think it's essential, especially if your recipe already has some.



Feel free to ask more specific questions, if the results aren't what you'd want them to be.