Can bushes help keep driveway and patio gravel stable?
Since there is an area of direct contact between the patio and driveway, the bushes won't serve as a separator (between your &quot;two distinct species of gravel&quot;) there. They will not, of themselves, &quot;contain&quot; the patio gravel, either - it can be kicked into them easily. For both of those reasons I would suggest some sort of &quot;hardscape&quot; (brick, paver, etc) edge completely encircling the patio to serve those functions. At minimum an edging strip.
Bushes will help to stabilize the slope and can certainly be planted on a slope. Choose the right (fruiting) bushes and they can also provide a snack at certain times of the year.