As far as I know Ilford rapidfix has no hardener, and I have been using it exclusively with all 35mm and 120 films without problems. I mostly use Ilford films, but other kinds like Kodak (which recommends hardener) and assorted others as well - all with NO ill effeect and negatives that are perfectly durable enough in my opinion.
Not many people use hardener these days, but if you want to, Ilford's Hypam fixer can be used with an additional Hypam hardener. They say not to use a hardener with Rapid Fixer. Data sheets at www.ilford.com.
I have used Ilford rapid fixer for more than four years on 35MM and 120 films of Kodak, Ilford and Fuji without problems and some negatives are handled a good bit. You could add hardener, but why bother?
"Nobody is perfect! But even among those that are perfect, some are more perfect than others." Walt Sewell 1947