Is the supplication of an oppressed disbeliever answered, and if it is, how do we reconcile that with the condition of Tawhid (monotheism) for supplication?

The supplication of a disbeliever may be answered for reasons and wisdoms known to Allah the Almighty, among them being the supplication of the oppressed. Indeed, there is no barrier between his supplication and Allah, as the Prophet (peace be upon him) said: "Beware of the supplication of the oppressed, even if he is a disbeliever, for there is no barrier between it and Allah." Allah answers the supplication of the distressed and the oppressed, even if they are disbelievers. Allah may also answer the supplication of disbelievers if they ask Him for provision or if they are afflicted by harm at sea, for at that moment they believe in the One they call upon and seek refuge in Him.