If Two Cryptocurrencies use different curves, Can They be in the same HD Wallet? I was looking through some code for HD Wallets and I saw that they used curve param.N which is specific for whichever curve is used.

Does this mean that when using HD Wallets to derive Private keys, they also need to account for the curve?

I know that they need to account for the curve when going from private to public. However, let's say that we were only deriving child private keys, can this be done without knowledge of the curve?
You can only do that if you are deriving hardened keys. For non-hardenend keys, you still need to know the curve as a public key is calculated for non-hardened derivation in order to derive the next private key.

Note that hardened derivation means that you will not be able to derive public keys from a master public key.