Why would re-entry waivers even come into the equation in your scenario? Re-entry waivers is when you are called UP not sent down, and that only applies to veterans of a certain age, which Sheppard has not reached.
Re-entry waivers have nothing to do with age. They have to do with how much you get paid. Basically anyone making more than $105,000 in the minors (basically any one-way deal) has to pass through them coming up from the minors.
Blog: First Round Bust: A Cast of Thousands celebrating a rather dodgy track record of Minnesota Wild Drafting.
"Will beats skill when skill doesn't have enough will."
Which is still besides the point. Sheppard doesn't have to go through re-entry waivers to go down to Houston. He'd go on waivers, likely clear... and be stuck there for the season. Re-entry waivers would never enter the conversation.