As part of HCB, you are operating as a project of The Hack Foundation. This means you are doing nonprofit work as part of a 501(c)(3) organization! However, a lot of companies don't extend their nonprofit discounts to fiscally sponsored projects.
While each company is different, a lot use third party nonprofit verification services. For example, a lot of tech companies use TechSoup to verify and provide nonprofits with discounted pricing. However, TechSoup cannot support fiscally sponsored projects.
When looking at companies nonprofit pricing pages, see if they explicitly mention fiscal sponsorship. If they use a third party verification service, check if that service has a policy for fiscally sponsored projects.
Ultimately, it's up the companies providing the nonprofit discounts to determine who is eligible for their discounts.