In Qatar it is not allowed to have two resident visa . If your visa is valid for more than one year Qatar immigration might ask you to cancell it . If it is less than six month or less then one year you can always says that it is automaticaly going to expire if you axceed 6 months away from Saudia . But entering Qatar on an employement visa with having Saudia visa is not a problem . It only be an issue when it comes to stamp Qatar RP on your passport . Here is the suggestion that when you enter in Qatar on work visa .
1. Complete medical
2. Complete finger print
3. Then apply your RP by e governament . Once you have approved by paying RP fees the last step is to stamp RP on your passport and get ur Id . And it can be done . Mail me if you need to know more about it ..