The Complete Peerage, 2nd ed., vol 12A, states that they were married between 28 Jan and 7 Feb 1449/50, and that they had a papal dispensation on 18 August 1450 to "remain in marriage, previously contracted in ignorance that they were within the prohibited degrees" citing Calendar of Papal Letters, Vol X, p. 472.
The Complete Peerage goes on to say that the marriage was dissolved before 24 March 1452/53 when the marriage of Margaret and the custody of her father's lands was granted to Edmund, Earl of Richmond and Jasper, Earl of Pembroke. Also referring to her second, third and fourth husbands.
I think that would indicate that the marriage took place and should be referred to in her biography.