Lounge access is available for Silver and Gold Members in all 100 destinations now so I cannot see any reason why it would not be available to you in BRU. If you are a Gold Member they will also give you an extra lounge pass for your guest if you are both on the same aircraft/route. Qatar may use Brussels Airlines Business Lounge, because they have a code share with this airline. However could be wrong so we will wait for the reply. It will also be nice to add the lounge to my 100 lounges thread.

I have tried to make a list on flyertalk that shows Qatar's 100 hundred lounges and have around 80 at the moment, maybe Alex can forward my list to the powers to be and ask them to put all the Qatar airport lounges on the official site just like some of the other airlines.