I see a fatal flaw: they will have dynamically
created pages for their members, to rotate the exposure
in much the same way as LinkExchange rotates banners.
Robots don't usually bother with "dynamic" pages
because the contents are not static, therefore don't
index cleanly.

Short term effect: invisible links with no effect,
and a lot of wasted effort, ofr most of the
search engines.

Long term effect: getting negative influence points
for being found on a page which is used
solely to bias the results.
It would be easy to request the links page
repeatedly, then whack the listed pages/sites with
some sort of penalty or give them the boot
entirely.

Max