I have never been attempted to be charged any taxes on a reward stay with IHG. The terms do not make an exception for per person or per night taxes. "Each reward is valid only for a double or king room for one night and tax." http://www.ichotelsgroup.com/h/d/pc/.../0/en/ptc.html

SPG allows hotels to collect per person/per night taxes from members, IIRC. Some IHG properties may do the same, but it's not in the T&C that way.