Proxy oder was?

[Useless]

Here's where my complete lack of knowledge about this business reveals itself once again.

What is going on when a submitter's IP matches that of his host? I assume he or she is either using some type of proxy or has submission software installed on his or her server. Am I warm? I've seen this a few times in the past, and I used to instantly black list for anything I didn't understand, but I have a new submitter doing this, whatever this is, so I'm wondering how leery I should be about the situation.