You are theoretically correct, but in this specific case name of PMC Wagner was taken by association with Nazi and founder of PMC is neonazi. 88 in Russia means the same as in all white supremacist groups — Hitlergrüß (HH).
Also, "88 = Heil Hitler" doesn't make a lot of sense in Russian, since H is not the 8th letter of the Russian alphabet (it is Ж, normally transliterated as zh), and "Heil Hitler" in Russian is хайль гитлер – х is the 20th letter of the Russian alphabet not the 8th.
14/88 doesn't make a lot of sense in Russian, doesn't stop it from being plastered all over the place by different militias (Including, but not limited to, Wagner).