I think that no need to buy 旅遊保險 to the maid.
If any accident out of Hong Kong for the helper, it's not the employer's responsibility.
Assume you take the vacation from the company and plan to travel overseas, will your company help you to buy 旅遊保險? ...
“the revised standard employment contract introduces on 1 April 2003 makes it clear that, under the new contract, employers are not responsible for providing free medical treatment during the period when the helper leaves Hong Kong of his/her own volition and for his/her personal purposes e.g. on home leave.”
Extract from the Guide of Employing Foreign Domestic Helpers issued by the Labour Department