The only way this goes any type of distance is if Mayweather allows it to rig the betting. Also there is scuttlebutt that McGregor wants to try his hand at boxing afterward rather than MMA because of the pay outs are higher, so I won't disregard the thought that there might be a little fixing that way.
As far as Malignaggi vouching for McGregor? He's getting paid, plus, while he's been a World champion, he himself is light years below Mayweather talent wise.