We are paying this following the RAW. As a counter is an attack, a squadron cannot counter Rudor if is engaged with other squadron.

Are we right?

Correct, counter attacks can never be made against Valen if you can engage the enemy.

1 hour ago, ovinomanc3r said:

We are paying this following the RAW. As a counter is an attack, a squadron cannot counter Rudor if is engaged with other squadron.

Are we right?

Yes.

Counter is an ATTACK, same as your "regular" attack, so anything that applies to other attacks applies to counter.

so does this rulling also work with escort? For me it is just weird but RAW say so.

Escort says "non-counter attack" specifically.