Dear,
If the company is providing family visa (either for expats or else one), medical insurance is obligatory for the issuance of Iqama (residence permit). But, its all depends on company policy & employment terms of the particular employee that whether the company will be responsible for getting the insurance done or the employee himself. In case of GOSI, it is for employees only. Also, GOSI (General Organization of Social Insurance) is not a medical insurance. So, in the discussion, GOSI doesn't has any specific role.
Continuation to the discussion, the word "family or dependent" does not stand only for spouse. It should cover for all the family members (for male dependents up to the age of 18 and for girl child till marriage), as per the Saudi Labor Law.
Thanks & Regards,
Prabhat Mishra