Afaik, you can if it is indeed owned by a different person and can be proven. But in your case, both accounts are actually yours so the above rules apply. Even if you do it secretly, I can't guarantee whether your 2 accounts will be fine forever. Especially if you have made a lot of withdrawals to the same address.

Actually, they force US users from Binance.com to use Binance.us they only allow to transfer funds from Binance.com to Binance.us but they don't allow to transfer from Binance.us to Binance.com.

If you want to transfer something from Binance.us I suggest you convert or exchange them for other coins to get cheap fees and send it to another wallet and then transfer them to Binance.com.

Or withdraw your bitcoin and use a mixer and transfer them to Binance.com so that they can't track your transaction.

Don't contact them. You can't use Binance.com if you are from (or in) the US, so they will just block your account if they find out. Just use your VPN when using .us and you should be good.

Where are you currently residing though? It's not sending the funds from one account to another that you should be afraid of, because it's probably okay to have an account in both exchanges, however, I wouldn't be surprised if one of the accounts gets flagged due to the IP address. Either way, I would highly suggest you write an email to the support team, just to get things cleared out.

If I understand, by users, you mean you have two separate accounts on the two platforms and wish to know if you can transfer between them?
Are you a U.S citizen, cause I remember U.S citizens had their binance.com account blocked and needed to transfer funds to the U.S based platform.

Yes, ideally transfers can be made between both platforms as normal.