Multiple link types per domain / engine

I'm trying to tune up some of the existing engines and add a couple more to increase my hit rate and find some more targets. It's lead me to a couple of questions as to how SER identifies sites when there are multiple engines that could be matched.

For example, if we look at Drupal there is a Blog engine for posting articles, and Drupal footprints in the 'Blog comments - General' file, as well as a possible match in the trackback2 engine.
In a case like this where a site could be listed under either engine, how does SER decide which engine should take priority when adding a domain, or does it add it to all engines where there is a match?

Also, I've noticed some engines - eg BuddyPress - allow multiple link types per domain. It initally creates an account, then tries to post an article in a group, which may or may not be successful. Then, it posts a status update with a link, using the script under [EXTRA_STEP1] (which doesn't seem to be documented)

Is there any specific reason to do it as one single script like buddypress, or as multiple scripts like the drupal example, or does it really make no difference (bar reusing accounts/saving on emails)?

Many thanks!