Are the outputs of an unconfirmed transaction part of the global UTXO pool? Well basically that. If a transaction is in the memory pool, that is, it is not yet in a block but nodes and miners know about it and validated it, Can I send another transaction that double-spends the outputs? that is, are the outputs considered unspent?
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.