And certainly, even if some may have been escaped slaves, they could never have committed "treason" against any states that did not even recognize them as citizens, just as any US citizen today could never commit "treason" against another country of which he was not a citizen, even if he was a resident of that other country. Treason first requires citzenship and allegience.
Slave-holding states in fact didn't even count slaves as fully human in population counts for congressional seats. To be a citizen requires that the state first ackowledge an individual is owed certain unique rights and privileges of citizenship. It would be impossible for any slave to be a citizen of any state that did not first recognize him as a legal citizen, and therefore it is impossible for a slave to be a traitor to any state that did not recognize his status as a citizen.
To recognize these soldiers as "traitors" to a state, would therefore mean they would have to be first publicly recognized as human beings, and as legal citizens of that state.