You are correct. You may play Unholy Strike to increase the Ranged or Melee attack generated by the Recruit action by 2.
However, since Recruiting Gosho does not generate a Ranged attack (his Interrupt does), the Unholy Strike will have no effect.
There are two ways this can work out.
Sequence A:
1. Recruit Gosho. 2. Interrupt the Recruit action with Unholy Strike. Unholy Strike fully resolves and does nothing, as there is no pending Ranged attack to increase. 3. Other player has the option to Interrupt the Recruit action. 4. Interrupt the recruit action with Gosho, produce Ranged 3. Fully resolve Ranged 3.
Sequence B:
1. Recruit Gosho. 2. Interrupt the Recruit action with Gosho. Produce Ranged 3. Fully resolve Ranged 3. 3. Other player has the option to Interrupt the Recruit action. 4. Interrupt the Recruit action with Unholy Strike. Unholy Strike fully resolves and does nothing, as there is no pending Ranged attack to increase.
Tsuruchi Gosho reads:
Thunder Absent Interrupt: After you Recruit Gosho at this battlefield, Ranged 3 Attack.
AFAICS That creates a delayed effect that resolves after the Recruit action resolves. So in Sequence B, there would be a ranged attack pending to increase. Or can Unholy Strike not increase pending ranged attacks?