This might all be true but it's hard for me to believe that anyone would have entrusted any matter of importace to either Oswald, Ruby OR Tippit.
I have always found this argument curious, though I've never heard it applied to Tippit.
While in the Army Air Corps, Ruby was an aircraft mechanic for three years. After he moved to Dallas, Ruby worked his way up in the nightclub business to become an owner. Castro's people in the U.S. trusted him enough to let him engage in gunrunning for them. As Mafia men went, Ruby was just as capable as anybody else of shooting Oswald with a pistol at close range, and actually Ruby was a smart pick because of his extensive connections with the Dallas police department.
As for Oswald, he was not entrusted with anything--he was set up, and by all accounts he was frequently being checked on and guided by those who were using him. In any case, Oswald was very intelligent, read a lot, and spoke Russian fluently. In the Marine Corps, he qualified for a high security clearance and worked as a radar operator for the U-2 program at Atsugi Air Force Base, Japan. People who knew him well said he was quite intelligent and an avid reader.
Regarding Tippit, he was exactly the kind of dirty cop that might be asked to shoot a patsy.