Frank, unfortunately, someone saw the post and has claimed it. If it falls through, I'll let you know.
In answering your question though...yes, it's a hole. For what, I have no idea. Done by previous owner. But it shouldn't affect anything. And I'm located in Queens, NY...11355. I think the sump was slightly wider than 12", otherwise, it was your fit.
Check out Jung's (gforce)...great guy to work with. And took a glimpse of the sump...great condition.
Thanks.