"Wallet" is kind of the wrong term to use. The address is associated with the genesis block (block 0) and is unspendable per the consensus rules. (edit: I'm wrong on that last point, see https://en.bitcoin.it/wiki/Genesis_block)
No it isn't. The 50 bitcoin created by block zero are unspendable (because by intention or error the software never passed block 0 through the validation logic that would enter those coins into required data structures).
But any other payment made to that address/pubkey are perfectly spendable by whomever has the matching private key.
Though that misunderstanding is somewhat common, so it's not impossible that the payee believed that they were sending the coins to an unspendable address.
Dead wallet means the private key to it is likely lost so nobody has access to it. Though there's always a chance someone actually still has it, so you can never say with certainty that a wallet is dead.
As for supply limitation, the current market cap of BTC is USD 860B, so this is 0.0001%.
> What means dead wallet? Might it be artificial supply limitation?
There are a number of addies with Bitcoins stored on them that are extremely unlikely (probability so tiny it's just zero for all intents and purposes) to be accessible:
This one for example (with a current balance of around $1.2k):
I don't think your second question makes sense. (Overall BTC supply? 1 million is a microscopic fraction of what's in circulation. 1 billion would be a little bit more interesting)