The one negative that I’m aware of planting blends of grasses (like milo, small grains, corn, etc.), with legumes (clovers, peas, beans, guar, etc.), and brassicas is that no single herbicide that I’m aware can be used without terminating at least a portion of the crop.
Never tilling and having a thick layer of mulch really helps with weed control, as can terminating any weeds before the crop is planted.
If grasses are the most prevalent competition a grass-specific herbicide such as Clethodim can be used as it won’t harm the broadleaves, legumes, or brassicas. It will take out the milo. Clethodim works best when grasses are less than 8″ or so tall.