48 years ago, I did exhaustive research on all ND men who played in the NFL...
I was just checking and found this list, from a Louisiana source.
1-Notre Dame - 513 NFL players all-time (11 Hall of Famers... Paul Hornung, Nick Bouniconti, Dave Casper)
2-USC - 438 ex. Trojans went to the NFL (11 made it to the Hall of Fame... Marcus Allen, Frank Gifford, Ronnie Lott, O.J. Simpson, Lynn Swann, Ron Yary)
3-Ohio State -378 players to the NFL (6 in Hall of Fame... Lou Groza, Dick LeBeau, Paul Warfield, Jim Parker, Bill Willis)
4-Michigan - 332 players to the NFL (6 in Hall of Fame)
5-Penn State - 325 in the NFL (5 in Hall of Fame... Jack Ham, Franco Harris, Lenny Moore)
6-Nebraska - 324 in NFL (3 in Hall of Fame)
7-Oklahoma - 296 NFLers (3 in Hall of Fame)
8-Tennessee - 290 to the NFL, tops in the SEC (2 Hall of Famers)
9-Pittsburgh - 287 in NFL (9 in the Hall... Mike Ditka, Tony Dorsett, Ricky Jackson, Dan Marino)
10-Miami - 284 players overall (5 in Hall of Fame)
11-LSU - 281 players (3 in Hall of Fame... Y.A. Tittle, Jimmy Taylor, Steve Van Buren)
12-UCLA - 278 players to the NFL (4 in Hall... Troy Aikman, Tom Fears, Bob Waterfield, Jimmy Johnson)
13-Wisconsin - 271 to the NFL (4 in the Hall of Fame)
14-Texas - 268 in the NFL (4 in Hall... Earl Campbell, Tom Landry, Bobby Layne, Tex Schramm )
15-Alabama - 267 in the NFL (7 Hall of Famers... Bart Starr, Derrick Thomas, John Hannah, Don Hutson, Joe Namath, Ozzie Newsome, Dwight Stephenson)
16-Michigan State - 263 went onto NFL (2 in Hall of Fame)
17-Purdue - 260 to NFL (4 in Hall... Len Dawson, Bob Griese, Hank Stram, Rod Woodson)
18-Georgia-259 to the NFL (2 in Hall of Fame... Fran Tarkenton, Charlie Trippi)
19-Florida - 255 in NFL (2 in Hall of Fame)
20-(tie) Texas A&M - 249 (1 in Hall of Fame)
---Illinois also with 249 (3 in Hall of Fame... Dick Butkus)
21-Washington - 241 to NFL (3 in Hall of Fame)
22-Iowa -235 NFL players (3 in NFL Hall of Fame)
23-Minnesota 234 in NFL (5 in Hall of Fame... Bobby Bell, Carl Eller, Bud Grant, Bronko Nagurski, Charlie Sanders, Leo Nomellini)
24-(tie) Syracuse with 228 (6 in Hall of Fame... Jim Brown)
---Auburn also with 228 in NFL (1 in Hall of Fame)
25-(tie) Arizona State 225 in NFL (4 in Hall of Fame)
---Florida State also with 225 (2 in Hall of Fame)
You may note that tiny Grambling State has four former greats in Canton, which is more than 13 schools from the above list and ties them with five other college football powers which also have four.
The late legendary coach Eddie Robinson did a pretty good job, didn't he?
By the way, it would not shock me to learn that our number is under-stated. There are a number of players who have attended ND for brief periods and become better known by their other school. I would have to see his lists to be able to comment further, but it seems about right.