Praise be to Allah.
Yes, it is permissible to use a truss during Hajj and also during ‘Umrah, even if it is stitched. It should be noted that when the scholars (may Allah have mercy on them) said it is haraam for a man to wear “stitched” garments (in ihram), what they meant was shirts or chemises, pants and the like. Hence we have to understand the words of the scholars as they meant them. Moreover, this phrase, “stitched garments” is not narrated from the Prophet (blessings and peace of Allah be upon him). It was said that the first one to use this phrase was one of the fuqaha’ of the Taabi‘een, Ibraaheem an-Nakha ‘i (may Allah be pleased with him). The Prophet (blessings and peace of Allah be upon him) did not tell the ummah not to wear stitched garments; rather he was asked: What should the muhrim wear? And he said: “He should not wear a chemise, pants, a head covering, a burnoose or khufoof (any footwear that reach above the ankle).” He did not use the word “stitched” at all. So we have to understand the texts as the speaker intended. End quote.