Would it be posible to install ODK Aggregate on DropBox?
I do not think ODK Aggregate can install on Dropbox, but you can (with ODK2) manage data to some extent on Dropbox by importing and exporting csvs.
To add to @elmps2018's answer...
You can't really "install" any of the ODK servers on Dropbox because Dropbox is online file storage with no support for the computing that a server requires.
If your goal is to get your data eventually on Dropbox, then the two ways I'd suggest are: