FOR THE HOUSTON CHRONICLE, the term is reserved almost exclusively for liberal action groups and inspector generals of government agencies of which the newspaper approves.
"Watchdog," of course, is an inexact term. In theory, any person or organization that digs up dirt on another person or organization could win the honorific title. For the Chronicle, however, it's a connotative signal of approval, a pat on the head, a "good boy" treat, a thumbs-up to readers.
A quick search for "watchdog" through the newspaper's search site turned up these examples on page one of the results: