I am not too sure on Jardine training Undertaker. From what I read - I believe in an interview with Gary Hart, Calaway was told by Bruiser Brody that he resembled Jardine; and that Calaway should study the Spoiler's act.
Regardless, if you watch the Undertaker in the last fifteen years, you are pretty much watching Jardine.
... Which is pretty darned cool. When I was a kid, Spoiler was my absolute favorite.