An ADS-B In/Out ACAS would need to know where it is but ADS-B Out going to TCAS has no need to know the integrity of the GNSS resolved position. See ACAS Link "
ACAS II works independently of the aircraft navigation, flight management systems, and Air Traffic Control (ATC) ground systems. " and FAA piece above.
I feel we are straying towards area we should not in a public forum but it appears your understanding of Certified is quite different to mine. A GNSS receiver may have a Technical Standard Order (TSO) but Certification of the capability is different and where differing systems are installed and work collaboratively. The TSO is but part of the process as compliance with airworthiness regulations must be demonstrated.