The answer is 'in most cases'. If you look in the Marriott Reward Benefits area of the website, it shows that you are 'entitled' to lounge access if Gold. However, there are a few pointers to bear in mind:
1. Not all Marriotts have a Concierge Lounge (CL)
2. In many cases the CL is only open on weekdays ... this can mean Sun-Thu or Mon-Fri
3. If the CL isn't open (e.g. Weekends) or there isn't a CL, some Marriotts will give you breakfast vouchers
4. The CLs vary globally ... the one in Hong Kong is excellent, Sydney Circular Quay is nice, County Hall in London is excellent ... all should be available to Gold members
5. The major issue is consistency ... as a number of hotels are 'Marriott Brand', there is a considerable variance on how they apply the Marriott principles
Many posts are written on the MRI site giving views on certain CLs ... it would be worth doing a search or writing a specific post if there is one in particular that you are interested in.
I hope this helps