Hioki is a superb grappler. his last display, dispatching Lawson in two minutes was really impressive. He has dominated top grapplers in the past, but Sandro posseses a different threat. I just think is a difficult match-up for Hioki, because Sandro is a typical Nova Uniao guy, being a good grappler with good TD defense, but adding deadly power in his hands. Hioki is an all-offense fighter, and though his stand-up is decent, his stance leaves him a little too much exposed to Sandro's power. Hioki has a good chin and he can survive some exchanges, but he can have problems to get it to ground, as he had with Inoue.
You can discount Hioki, with his quick transitions and incredible guard passing skills, but he is gonna be in permanent trouble as much as the fight stays on the feet. Either way that fight is a must happen, being both top 5 FWs fighting in the same org.