Oman gives these notes on a possible marriage:
(Research):MARRIAGE: Investigate> Dwnn's 'Heraldic Visitations of Wales' volume 1 pages 297 and 314 give as his wife Arddun ferch Llywarch ap Loen ap Cilimin "Troedtu".
MARRIAGE: Investigate> Lloyd's 'History of the Princes, the Lords Marcher and the Ancient Nobility of Powys Fadog' volume 5 page 114 gives his wife as Arddun ferch Llywarch ap Lloen ap Cilmin "Troedtu".
MARRIAGE: Investigate> Evans' 'British Genealogist' book 6 page F43 gives his wife as Arddun ferch Llywarch ab Llywelyn ab Celynin "Treod-du".
CONCLUSION: Because of the generational timeframe separating Gruffudd and this Arddun it is highly improbable that she was his wife.