An 8(a) sole source award can be challenged at the GAO, but a protester will have a difficult battle showing that the sole source was a result of bad faith.
Source: 8(a) Sole Source Decision: “Bad Faith” Bid Protest An Uphill Battle – SmallGovCon
SBA Updates All Small Mentor-Protege Template with Affiliation Questions
With little fanfare, the SBA has updated the template for agreements under the All Small Mentor-Protégé