The active ingredient in Nizoral shampoo, ketoconazole, does have anti-DHT properties. Since hair loss at the scalp is related to DHT, using Nizoral shampoo can help offset the hairloss from AAS.
If you type in "Ketoconazole" and "DHT" into any search engine, especially Google Scholar or PubMed, you will find plenty of research.
You would want to use Nizoral daily while on cycle. If you experience any itching or redness of the scalp you may want to take short breaks from Nizoral use.