I've had a parasite infection for years (and am just now getting ahead of them with pharmaceuticals, for good I hope) and have used vitamin C extensively (IV, oral, and lipo). I've followed multiple protocols and have bowel tolerance-titrated many times (both to treat myself and to gauge my level of oxidative stress), and really have had nothing but good luck with it. I've had ~40 C IVs (up to 40g each) and on several occasions after about 10 C IVs - one every other day - all of my symptoms cleared up and I achieved a seemingly complete 'remission'. Just based on my experience, I would say that it's less likely the ascaris is stealing/using it and more likely your body is using it to 'quench' the free radicals produced by the infection (or some other pathology) and to strengthen itself, generally. Generally, I've never heard of C being used by a helminth and because I do better with C, my experience is contrary; however, it doesn't seem entirely implausible and I will likely do some more research on this topic. I'll let you know if I learn anything.
Consistent with what I've read (Levy, Cathcart, Klenner, Pauling, et al.), I've found that the higher my levels of oxidative stress, the more vitamin C I can take before hitting the bowel tolerance threshold. Also, the higher my serum concentration of vitamin C (e.g. following an IV), the more I can take orally. For instance, I may normally be able to take 12-15g of C orally, but following a 30g C IV, I can take 50-60g before it's 'too much'. This makes sense when you consider relative concentrations on either side of the bowel wall and how the body deals with oral 'overdoses' (like with epsom salts as a laxative).
I know that Ivermectin should not be taken with fruit juices, generally, as they reduce uptake and serum concentration, though I've not heard of similar with Albendazole or any other anti-helmintics (pharms, herbs, or otherwise). In fact, I've seen C recommended as an adjunct to antihelmintics, generally, in multiple places.