Okay after doing some tests a few nights ago I’ve found out a few things:

*Yes it is true that posts with regular links to non-tumblr sites won’t show up in searches.

*Posts to a page on your tumblr blog with links to non-tumblr sites will show up in the search.

*However what I find more interesting is if you make tumblr re-direct links through your customize blog page to non-tumblr sites and put them in your posts those posts will still appear on Tumblr search.
Special thanks to Adurot for pointing this out to me via Clone That got Away. Here’s a link to the reblog that explains how to do it.

I’ll probably most likely be going with the third option for future art and comic posts.