What is the ruling on bringing in Buddhist or Christian foreign workers?

The default rule is the permissibility of hiring non-Muslims and bringing them in for work. Evidence for this is found in the actions of the Prophet (peace be upon him) and Abu Bakr. It is, however, good to prioritize bringing in Muslim workers if possible, as a form of assistance to them. If a Muslim brings in a non-Muslim, it is imperative to treat them kindly, fulfill obligations towards them, and strive for their guidance, while being careful not to allow them private seclusion with women, or to instill their false beliefs in the minds of children, or to permit them to use devices in a forbidden manner.