There seems to be no direct link between the two arts. There is certainly a dearth of evidence to support such a link.
The thing that gets me is that people seem to think that because Daito Ryu and Ba Gua use circular movements, they must be related
The fact of the matter is, as far as I know, that there are as many linear techniques in Daito Ryu as there are circular. And Daito Ryu Aikijujutsu is an amalgimation of various arts studied by Takeda Sensei, most notably those arts of the Oshiki clan. So you can't really say is Aikijujutsu similar to Ba Gua, when Aikijujutsu has such a broad palette of koryu running through it.
Another point. Most styles of traditional Japanese Ju Jutsu also have circular techniques. This feature is not unique to Daito Ryu! Most also deal with multiple attacker situations. Again, this is not common to Daito Ryu. So why is Daito Ryu alone singled out as being similar to Ba Gua? Did all samuari learn Ba Gua, collectively return Japan, then simltaneously develop seperate ryu ? Such an occurence is highly unlikely in the extreme to say the least!!
IMHO any similarities are merely conicidence. Both arts employ similar principles in a FEW areas, but they have far more differences than similarities. They likely had some similar school of thought that influenced them millienia ago, but such things are lost in the mists of time. You could say that is true of all martial arts I suppose.
But as I said, there is no tangible connection between Ba Gua and Daito Ryu.