I would love to do this with Saban/Miles and others, the problem is using Rivals (my arbitrarily preferred information provider) I can only find data back to 2002. Beyond Petrino and now Sumlin, I don't think that one could do a similar analysis.
I would love to find Saban and Mile's recruiting data before they both went to LSU. It is more complicated than that, obviously, because I need the recruiting data for everyone they played too.
Such data exists, but it is spread out across various print publications, recaptured in various websites across the web. One way one can infer their recruiting success is to look at the number of NFL players they landed on their roster during their tenure.
Saban
1990-1994: 5 years pre-Saban
Total: 14 players 2+ seasons in NFL
Average: 2.1 NFL players per recruiting class
1995-1999: Saban's 5-year tenure
Total: 14 players 2+ seasons in NFL
Average: 2.5 players per recruiting class
Upshot: Saban slightly improved Michigan State's recruiting success compared to the norm at the program, but wasn't building a top-tier program there.
Per Miles @ Okie State,
1997-2000: 4 years pre-Miles
Total: 6 players 2+ seasons in NFL
Average: 1.5 players per recruiting class
2001-2004: Miles' 4-year tenure
Total: 9 players 2+ seasons in NFL
Average: 2.1 players per recruiting class
Upshot: Miles slightly improved Oklahoma State's recruiting success compared to the norm at the program, but wasn't building a top-tier program there either.