Are the outputs of an unconfirmed transaction part of the global UTXO pool?
The transactions are considered spent from the nodes that already have the transaction in the mempool, that is, if you try to double-spend the transaction, they will reject the new one. However, if the transaction ends up not being included in a block, they will be dropped from the mempool after a certain time. After that, you will be able to create a new transaction that spends the same UTXOs, since from that point on it won't be considered double-spending.