From Bob Masullo:

An analysis of 2002 major league baseball rosters shows IAs have a fair 
representation on the field and better than their share of team manager posts.

(Note: Based on Italian surnames; IA players/managers without Italian 
surnames are not included. If you know of any, please message me. 
(MasulloYankees @aol.com)

There are 35 IA players out of a total of 750 major league players. That's 
about  5%, approximately the same as the percentage of IAs in the US.[RAA 
Note: That figured is base on 15 million I-As, wheras some 
authoritative sources cite up to 25 million I-As, or 8%]

There are 4 IA managers our of a total 30 managers. That's about 13%.

Italian American Major League Baseball 
Players and Managers in 2002

AMERICAN LEAGUE

Anaheim Angels
1) Scott Spiezio, IF
(Mike Scioscia, MGR)

Baltimore Orioles
2) Marty Cordova, OF

Boston Red Sox
3) Doug Mirabelli, C

Cleveland Indians
4) Chad Paronto,P

Chicago White Sox
5) Mike Porzio, P
6) Tony Graffanino, IF

Detroit Tigers
None

Kansas City Royals
7) Joe Randa, IF

Minnesota Twins
8) J.C. Romero, P
9) Jay Canizaro, IF

New York Yankees
10) Mike Mussina, P
11) Jason Giambi, 1B
12) Robin Ventura, 3B
(Joe Torre, MGR)

Oakland Athletics
13) Mike Magnante, P
14) Mike Venafro, P
15) Barry Zito, P
16) Frank Menechino, 2B
17) Jeremy Giambi, RF

Seattle Mariners
None

Tampa Bay Devil Rays
18) Jason Conti, OF

Texas Rangers
19) Frank Catalanotto, OF

Toronto Blue Jays
None
 

NATIONAL LEAGUE

Arizona Diamondbacks
20) David Dellucci, OF

Atlanta Braves
21) Mark DeRosa IF

Chicago Cubs
22) Jeff Fassero, P
23) Joe Girardi, C

Cincinnati Reds
None

Colorado Rockies
None

Florida Marlins
None

Houston Astros
24) Craig Biggio,IF

Los Angeles Dodgers
25) Paul Lo Duca, C
26) Giovanni Carrara, P

Milwaukee Brewers
27) Mark Loretta, 2B

Montreal Expos
28) Carl Pavano, P

New York Mets
29) Jeff D'Amico, P
30) Mike Piazza, C
(2 Bobby Valentine, MGR)

Philadelphia Phillies
31) Ricky Bottalico, P
32) Cliff Politte, P

Pittsburgh Pirates
33) Ron Villone, P

St. Louis Cardinals
34) Mike DiFelice, C
(10 Tony La Russa, MGR)

San Diego Padres
None

San Francisco Giants
35) Rich Aurilia, SS