Actually, the no one really knows the true parentage of dominii, dominiana or intermedia. We can only take educated guesses based on what these plants look like.
Dominii was originally made by John Dominy in 1858, and officially named in 1862. In 1862, N. hirsuta had not even been described yet. It was first described by Hooker in 1873.
However, the Veitch and Son catalog in the 1890's describes dominii as a hybrid of N. rafflesiana x "an unknown Bornean species". The illustration shows a plant that looks just like what you would expect from a hybrid of raff x gracilis. The later hybrid, N. intermedia was made in the late 1870's, also from an unknown Bornean species, and it looks like N. raff x N. hirsuta. I have personally seen two different clones of intermedia, and they do not look like the illustrations and photos I've seen of N. dominii, even though some of the older literature refers to N. dominii and N. intermedia as the same thing. I beg to differ. As far as myself and several other Nepenthes growers are concerned, the 'true' N. dominii would be a remake of John Dominy's 1862 hybrid, which most likely used a N. gracilis. There is no doubt to myself that Dominii (or dominiana: the same thing) and N. intermedia are two different hybrids. Even though Dean Cook's plant is most likely a remake, it looks like the illustration of John Dominy's original cross.
Whew!!!
Trent