A mindmap offers a visual representation of a tree/graph of text items. It makes it easy to change the point of view (move around, fold/unfold).
A wiki offers a page-based view of hyperlinked text. Typically one page of a graph of pages is visible at a time. Publishing and sharing is very easy with a Wiki.
Instead of hosting mindmap files on a wiki, it seems interesting to map a mindmap to a bunch of wiki pages.