Ah, the rewrite_get_album_image() is pretty much what I thought was going on, but I didn't know where to find it.
I have gotten it to work now by adding another param into my mod_rewrite and ignoring the function that checks the url in rewrite_get_album_image().
As far as why I'm doing this, it's because the site I'm working on needs duplicate projects in multiple categories (which I'm doing with tags) but also has a highlighted navigation which needs to reflect where the user is. So if a project exists in the root and that's where it's getting re-directed then that doesn't work since it'll lose its context. So now, the mod_rewrite works like this:
RewriteRule ^(cat1|cat2|etc.)/+?([A-Za-z0-9_\-]+){1,}/?$ index.php?album=projects/$2&category=$1&project=1 [L,QSA]
RewriteRule ^(cat1|cat2|etc.)/?$ index.php?album=categories/$1&category=$1 [L,QSA]
RewriteRule ^(.*)/?$ index.php?album=$1 [L,QSA]
So I can just put all my categories into an album called categories, and all the projects into a projects album, and do the rest with tags.