This is true, except in scenarios where the evil team has Oberon in the team, so doesn’t know a second evil is there.
Like, hypothetical, let’s say that Rowe is Oberon and Ot is the one of the other three evils. Then an evil player would have no idea a second evil was on the team. Or let’s say that Thraeg is Oberon. Now not Thraeg and Ot would know two evils are on the team, but no other evil would, and given Ot just ‘cleared’ Thraeg it would be highly suspicious to vote against a team with both of them.