In supermarkets in the United States, I tend to hear this often:
Cleanup on aisle two [or some other number].
Would in be as good as on? How is in different from on in this context?
I've heard both used. I think it just depends on whether you consider the aisle to be a place in need of cleanup ('in aisle two') or a surface in need of cleanup ('on aisle two').
This NGram shows that 'in aisle' is actually used more frequently than 'on aisle' in general, though that isn't limited to just the 'cleanup' usage.
In would be as good as on. The way in which they differ in this context is nothing more than a convention that people say on more often than in:
This is like asking if “Happy Christmas and Merry New Year” would be as good as “Merry Christmas and Happy New Year”. Sure it would. It’s just not what people say.
It occurs to me that this is not a practical question based on an actual problem. In its essence, this is a question about something that nobody does. There is nothing to be explained here.
Probably "on" is most common because it makes the most sense, semantically, if you think about aisles in a grocery. An aisle being a passage, items aren't placed "inside" of one because there is no inside; an aisle is an open space by definition.
"Cleanup needed on aisle 3." "The milk is on aisle 3."
These sound most natural because the shelves and products occupy and also serve as the boundaries of each aisle.