Does any one know the definition of a financial institution as it would pertain to Rev Proc 2003-16? Wondering if the definition includes recordkeepers.

A financial institution is almost always defined by the government as a depositor institution as defined by the Federal Deposit Insurance Act, any federal credit union or State credit as defined by the Federal Credit Union Act and any benefit association, insurance company, safe deposit company, money-market mutual fund, or similar entity authorized to do business by a State.

Unless the TPA is part of one of these organizations, it would not, in my opinion, qualify as a financial institution.

The list of IRS approved nonbank trustees and custodians is provided in Announcement 2002-12, which is available at the URL below.
Generally, speaking, financial institutions include banks and institutions in Ann 2002-12

http://www.irs.gov/pub/irs-irbs/irb02-08.pdf