Agreed bdcutler,
And would even go so far as to say that God not only uses the base things of the world to bring the message of the gospel, but even even wicked unbelievers mocking the (true)gospel, which is who Paul is talking about in Philippians 1.
Imagine being a Roman in 50 AD and hearing a man mocking Christ and Christianity (keep in mind you've never heard anything about Christ before). You really might be interested and seek out those Christians to find out more about Christ, and in so doing become a Christian yourself. I have heard of a few modern day cases where someone was saved through "the witness" of a mocker.
Consider these two passages:
Jews in Rome speaking to Paul- "But we desire to hear of thee what thou thinkest: for as concerning this sect, we know that every where it is spoken against." (Acts 28:22)
And Paul writing to the Romans- "First, I thank my God through Jesus Christ for you all, that your faith is spoken of throughout the whole world." (Romans 1:8)
That is very different than unity with denominations that preach salvation by works or a watered-down easy-believism. Paul rejoiced in good content even from a malicious witness and the Galatians 1 passage shows what his attitude was towards a false, perverted gospel- which we know is preached in many denominations. To those he said
"And have no fellowship with the unfruitful works of darkness, but rather reprove them." (Eph. 5:11)
See 2 John 9-11 also.