I don't think there is anyway to answer this question, and I dont think they would be, anyway.
In all of the instances of "obtaining" a Ride Pager Pokemon, they seem to simply appear in your possession. Nobody gives them to you. They just teach you the skills... Which doesnt make complete sense but oh well that's Game Freak.
And it wouldn't make sense for them to be from the Trial Captains in the first place for a couple reasons. First, in the example of Mudsdale, Hapu teaches you how to ride hers, but then takes hers back, obviously, it's her ace. And other Pokemon like Stoutland and Sharpedo are given to you by people who have no association with the trial Captains, (a farmer, and Grimsley.)
There's also a quote in the game that specifically states that a registered Ride Pokemon would come to you when you call them. The quote was written to indicate that there existed many Ride Pokemon of the same species... I'm sorry I couldn't find it. If anyone is able to find it, please comment below!
commented Feb 7, 2017 by !'•-Indigo-•'!
edited Feb 10, 2017 by !'•-Indigo-•'!
I remember this quote too, so after all of this evidence I am confident that the Pokemon that appear from the Ride Pager are not the Trial Captain's
Hope I helped!