Dawson was released after 10 years at the club and subsequently joined former side Scunthorpe.
The Iron have a League Two fixture at Bristol Rovers on the same date as the Betis match, August 10, but Dawson has been given permission to play in his own testimonial instead.
The 34-year-old played 317 times for Hull and was part of four promotion-winning sides.
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? firstname.lastname@example.org