Does re-transmission really reduce security? I am using AES with GCM and a colleague told me "Repeating a VCC with the same key and a different message reduces the security of the key." He did not have any additional detail to offer.

What he meant was since the encrypted VCC is in a fixed location in a packet, bad guys could intercept the messages and correlate the two messages, somehow making it easier to crack the message or key because the VCC was repeated. (I don't understand how bad guys would know if the VCC was repeated or not...)

My understanding is the VCC is there to prevent replay attacks, nothing more, nothing less. I understand they should not be repeated.

So my question is this: does repeating the VCC with a different message and the same key actually make it easier to crack the encryption key? If so, how?
Your colleague is wrong; assuming that the GCM nonces are generated correctly (that is, never repeats for the same key), there is no risk to GCM in repeating the VCC.

GCM has the property that, as long as you never repeat the nonce for the same key, GCM guarantees both the privacy and integrity of the encrypted plaintext (assuming that AES is a strong block cipher and that the AES key cannot be guessed).  This remains true even if you repeat the same region (such as the VCC) for multiple plaintexts.  Actually, the guarantee is even stronger; you could let the attacker choose the plaintexts for you to encrypt, and he still cannot learn either the AES key, or the plaintext for an encrypted message that he did not choose.