Lets put it this way.
-Roll might possibly be one of Lucario's best oos responses.
-retreating roll =/= approaching/cross up roll
-There are options for when you're retreating you can still do stuff like a retreating fair
Basically, it really is more of a style thing, it definitely works as long as they don't have a ridiculous long range punisher like AS, banana, zair, or something, but remember that you could also be doing something at the same time while they're pressing in on you, and that you can only retreat so much before you have to cross up or do something :\
I notice when I was in my roll-happy stages, if I start making my style and zoning more spacing intensive, roll habits tend to disappear, because you need the flexibility that your walling/zoning tools give you, something roll can't do because it's a fixed movement.