... Vidal Jarbeaux cannot use Summoning (at superior Presence) to recruit (indirectly) an ally for which he doesn't have the requirement without using of his special ability, e.g. a Nephandus or an Arms Dealer.
The reason is that Vidal is not playing the ally directly (so the text of his special ability cannot be applied). The ally card simply isn't played (for the same reason you cannot play Direct Intervention on the ally summoned). In principal, for the same reason this prevents Vidal from getting weapons via Disguised Weapon or Concealed Weapon for which he doesn't meet the requirements (e.g. Femur of Tomler or Sword of Troile).
Reference: VtES Usenet Newsgroup.