Few questions...

I could not find any bro mailing list archive.

(it's available as a single flat file [:-(] by sending "get bro archive"
in the body of a message mailed to majordomo@lbl.gov)

Does bro detects illegal TCP acknowledgements and
retransmissions which i could not see using ordinary
dump utility?

Depends what you mean by "illegal". It detects acknowledgments above
sequence holes, and inconsistent TCP retransmission. Unfortunately, when
looking at a large volume of traffic, these show up due to various things
being broken (as mentioned in the Bro paper), so their presence isn't
a useful indicator of an attack.