and also the size of the refugium you plan to add. If the refugium adds enough water volume and has some live rock in it, then I would say yes, but it is hard to say with the information provided.
I agree with with Matt...With adding a fuge, you will be increasing water volume etc which will allow you to be able add another fish or so depending on the water volume you add, type of fish you want etc.
Oops! I guess we were posting the same time(LOL) The yellow tang would be "up in the air" in my opinion personally unless you get a small one. I have a yellow tang in my 75 gal now and I'm going to have to part with him soon when I make my change over to the cube I'm getting. They seem to love a lot of swimming space, but I couldn't say for sure if it will be a problem for you or not. The goby's I think would be definately fine though...Just my 2 cents.
what size is your tank, yellow tangs need at least a 4ft long 55 gallon tank or bigger, fuge doesn't help with fish's required tank size but helps with the bioload they create