The phrase "hardly more elusive" suggests that the Abominable Snowman (also known as the Yeti), who is believed to haunt the imagination of climbers in the Himalayas, is not significantly more difficult to find or capture than something else that is already very elusive. Essentially, it implies that the Abominable Snowman is just as difficult to locate or encounter as another elusive entity or concept.

It would help to have more context. The writer must be describing something, call it X, which very elusive. He is probably discussing whether X really exists. The writer is comparing X to the Abominable Snowman. The writer strongly doubts that the Abominable Snowman is real. The writer doubts that X is real. Something--in this case evidence, or proof--is "elusive" if people keep trying to find it, but never do. Perhaps they try to take pictures, but the pictures never come out or are too blurry to prove anything. Nobody has found proof of the existence of the Abominable Snowman. Proof has eluded them. The writer uses the Abominable Snowman as an example of something that is extremely elusive and is probably imaginary. The writer says that X is as elusive as the Abominable Snowman. He "hedges" his language slightly. "Hardly more elusive" means that the Abominable Snowman might be more elusive--but only slightly. The writer means something like this: "It's crazy to believe in the Abominable Snowman and believing in this is just as crazy."