Just check the frame data to see if it's guaranteed, although D3 on crouch hit is +7.
If you're too lazy for that: D3 is guaranteed except 6 frame moves, the game doesn't allow trades and will randomly assign a winning hit when moves are done at the same time. D1 on stand hit will not give you a guaranteed D3. If your D3 hits if the opponent is standing, F3 is not guaranteed since a 6 frame move will also randomly win. On crouch hit however, F3 is guaranteed. If D3 is blocked, F3 is definitely not guaranteed.
This is all on paper though, it's pretty tough to do moves right down to the first possible frame.