Nearly there. The orphan pools serves primarily those without a parent transaction that can be found in their UTXO. For those transactions, they are stored in a orphan pool with a max transaction size of only 100, if I'm not wrong. You can't do much with it. Even if you want to spam up to their limits, its fruitless and it won't be relayed to other nodes.
Thank you. What happens when it reaches the limit. Drop existing transactions or refuse new coming transactions. I think although the spams won't affect other transactions, it will somehow interrupt the service of orphan pool.