Since there are not enough doctors and nurses, the imported of foreign healthcare workers will not increase the number of unemployed population. The problem remains is whether these imported workers are included in the calculation of labour force.
According to the HKSAR Census and Statistics Department, the employed person (or employed population) comprises those persons aged 15 and over who have been at work for pay or profit during the 7 days before enumeration or have had formal job attachment.
Since the imported workers get paid $31,000 per month, are definitely aged 15 or above and will probably work for 7 days and longer, they are regarded as employed person. So, labour force will increase and the unemployment rate will decrease.