How can this not be shounen ai? It's published in a BL magazine and even the mangaka has it under the BL tag in her blog. And the subtext, oh the subtext!
I have a feeling that this will turn into true BL at some point. As you've said, the story is being published in a BL magazine and the subtext can be felt from 5 feet away from the pages. We'll just have to see. I wish the next chapters would get scanlated soon, but it doesn't look like that's going to happen. The scanlator, Moon in a Box, deleted their livejournal and may not do scanlations anymore. If that happens, I hope someone else will pick up this story.
As you may know by now, Dear Brother is being continued by a group of former MIAB-ers plus a former MIAB fan/member. The latest chapter, chapter 5, shows very clearly that this is Boys Love. The person who kept taking the Boys Love (or yaoi) tag off of the Manga Updates article was clearly off her nut.