Yes. 100%. Anyone who says otherwise doesn’t know what they are talking about.

If you want a longer answer, it’s practically exactly the same as if you put bitcoin into a multisig where you held a key, and then pre-signed a transaction to send it to yourself and simply didn’t send it yet because you wanted to keep it in the multisig. Can you put counterfeit bitcoin into a multisig address? Of course not. Can you sign and broadcast a transaction with bitcoin not in your address? Of course not. Is there anything about the multisig that makes the bitcoin less real? Obviously no.

People who know nothing about Lightning say this.