"I suspect my wife has commited adultery and want to know if i can subpoena her friends and the person she is secretly seeing to prove adultery?"
*** Yes, you can subpoena him. However, since his admission would be to a crime, he would be a fool to answer your questions.
"What are the pro's and con's of such actions?"
*** In addition to your wife being able to question YOU as to your actions, see above.
§ 28.221 (MCL §750.32) Cohabitation by divorced persons as adultery
If any persons after being divorced from the bonds of matrimony for any cause whatever, shall cohabit together, they shall be liable to all the penalties provided by law against adultery.
§ 28.219 (MCL §750.30) Punishment; application to unmarried man
Any person who shall commit adultery shall be guilty of a felony; and when the crime is committed between a married woman and a man who is unmarried, the man shall be guilty of adultery, and liable to the same punishment.
Statutes can be found at:
http://michiganlegislature.org/law/mileg.asp?page=getObject&objName=mcl-328-1931-V&highlight=