In OTL, Hideyoshi was a member of the Black Dragons.
I wonder how long Minoru can last once Atsuko gives birth to a heir.
This time around, he´s in a position very close to Minoru, closer than any Black Dragon in OTL, and Minoru trusts him, more so than OTL Theodore trusted him or any of the other Black Dragons. He might feel that being able to mold Minoru and his heir is preferable to risking exposure in a plot to murder Minoru, successful or not.
Plus, right now (unlike during the OTL attempt on Theodore in 3058) the Combine is against the ropes, so he might not want to risk a civil war against those rallying behind Omi (and/or Franklin), or even just purges of likely Omi/Franklin supporters in the military.