Your question leaves out a lot of facts. Why would any kind of shuttle or bus service run a check on people getting on a bus. It seems a little silly to me. Perhaps I am missing something. If you are concerned address this to a criminal defense attorney in your area.
Bus services have security people checking parcel shipments for drugs like UPS and Fed Ex do. I have experienced cases where local police have asked the local terminal to watch for a certain person traveling in or out. I am not aware of any systematic screening of all passengers for warrants and have not yet had a client arrested in that process when traveling by bus. I have had clients arrested when flying commercial.