Are you saying there is Gnosticism in the works of Tolkien, or just that the Gnostics have misappropriated/used his works toward their own ends?
They love Tolkien for several reasons:
- Tolkien's fantasies are based on his "mythopoetic" Silmarillion, the origin of which they accept as a truely gnostic source ("genuine experience" like "that of C. G. Jung's").
- Tolkien's fantasies are based on a cosmogonic/cosmologic myth which resembles the elaborate manichaean dualistic cosmogony/cosmology.
- Tolkien's fantasies are peppered with gnostic ideas.
If you want to read the Silmarillion, I recommend you listen to the following interview first, in which gnostic scholar Lance S. Owens explains this in more detail:
"J.R.R. Tolkien, C.G. Jung and Gnostic tradition." (audio) A link to the audio can be found on the following page:
gnosis.org/tolkien.
I don't think it's possible to accuse them of misuse of Tolkien's work. Owens says that Tolkien had no contact to esoteric agencies, but that he delved into Alchemy, Hermeticism, Kaballah in Zürich in the 1930s, and he mentions the hardly deniable influence of the occultist Inklings Charles Williams (Fellowship of the Rosy Cross), Owen Barfield (Anthroposophist), and Robert E. Harvard (Freudian analyst, Tolkiens lifelong personal physician).
Whether one does or does not care about what Gnostics say, the dualistic cosmogony in the
Silmarillion (Owens interview 18'41"), the dualistic
reality of evil instead of Catholic
evil is privation of good (37'25"), as well as other gnosticisms are present in Tolkien's work.