Multisig addresses are like any other address generated from independent spendkey and viewkey. In fact, there exists some spendkey which lets you spend from it alone, but nobody knows which one of all the possibilites it is. Same like nobody can tell a spendkey of a regular wallet.
Can a normal Monero seed produce the same address as a multisig wallet?
Probably no. That's because the view key is not derived from the spend key.
For the second part of your question, it's possible to create such a wallet. Not by using the seed, but by using the keys.
For N/N, it's as simple as taking the same viewkey, and adding the individual spendkeys together and using the result as the spendkey of this "master" wallet. Of course, you need all the spend keys for N/N.
The "master" wallet will be no different than any other wallet created by using --generate-from-keys option. All you need to do is compute the EC sum of individual keys and use the result for the spendkey.
In fact, PR-2218 makes a command-line option to do the above.