There are precious few people alive who've had the honor and opportunity to train with both Ueshiba and Tohei. My understanding is that at least two still reside in Hawaii, and one has already weighed in, saying that what Dan Harden is doing is in line with the aiki of Ueshiba. While I don't know this gentleman's specific take regarding what Dan is teaching relative to what Tohei expressed regarding aiki, if Ueshiba felt Tohei was on track regarding aiki, and people of the Tohei lineage here feel that IP/IS methodology (Dan's per se) is compatible with what Tohei taught, then all these data points support a clear relationship between the various methodologies, allowing for differences in flavor that would've been acceptable to Takeda and Ueshiba.
I have been studying with a gentleman who fits that bill since 1988 (Imaizumi Sensei). It is beyond comical when people who have no real history or affiliation with Tohei Sensei, or O'Sensei begin to tell us what these two men did, said, or meant. These same people also seem to have an affinity for talking about what Dan Harden does or does not do without ever having met him, let alone trained with him. I simply ignore the "white noise" from those who claim things that is obviously beyond what they should ever claim, and continue to train with Imaizumi Sensei and Dan Harden. Like you, reality speaks a lot louder than the chatter in some people's posts.