Can I use another app (wallet software) to transact with my ZERO?

No. For now, the ZERO can only communicate with the LIQUID app.

But we are working with other wallet vendors on QR code compatibility. You could then sync with other wallets instead of the LIQUID app via XPUB sharing with a standardised format for transactions. This way you can then use other wallets with more advanced configuration options, such as connecting your own custom node.