I have not worked with VDB particularly, but I will chime in based on my experience with selenium toned Centennial POP and more lately some salt printing. Speaking now only for selenium toning (not gold/thiourea,) there should be no reason to fix it again unless you have not fixed fully the first time. If that was the case, you will get stains from selenium toning so you will know anyway.
Some people seem to think that it is necessary to do hypo clearing after selenium toner treatment as it contains ammonium thiosulfate (assuming you are using KRST.) I am not sure why as ammonium thiosulfate is supposed be much easier to wash out than its sodium sibling. I follow my KRST toning with a 30 min. running water wash. Just to make sure, I checked with a residual hypo test on the print and the result was negative. So I did not bother to do any hypo clearing after toning. If you do, it should not hurt it though.