If the work is performed outside the US , and the recipient of the income are foreign persons, no need to withhold the 30% as you would if the foreigner has US connected source of income.
However, you will still need to request for W8 from the foreign person certifying that they are foreign persons receiving such income.
IRC 3401(a)? defined wages as ?all remuneration (other than fees paid to a public official) for services performed by an employee for their employer including the cash value of all remuneration (including benefits) paid in any medium other than cash??
Reg 31.3401(a)(6)-1(b) provides that ?remuneration paid to a NRA for services performed outside the US is excepted from wages, and hence is not subject to withholding?