What makes you think it is sending a General? I am pretty sure it is not tbh. Let's take a look at the tooltip again:
1. Sending a General should probably be grouped around Exp. Forces, Volunteers or Lend-Lease. But it is between improving relations and NAP. Furthermore: Why the hell should you be able to send a General in Peace Time?
2. The other side has no chance of accepting or denying. You can deny Volunteers, Exp. Forces or Lend-Lease, but not getting a General? Everything that kinda changes your country can be accepted or denied. That leads possibly to the conclusion, that only the sending country profits from the attaché, while the receiving country does not get anything. Even though the Tooltip says "Higher military cooperation", it also states "developing our (own) strength" . It leads possibly to a research bonus.