I think there are ways to spin Stripe's investment as a customer acquisition play. If they have more influence over Lambda School curriculum or partnerships by merit of being an investor, and Lambda School is churning out web developers whose first instinct is to turn to Stripe for all things billing, that seems like a pretty reasonable use of investor capital to me.

Someone made a similar comment about YC a few weeks ago – how if you were building dev tools, even though $150k for 7% results in a lower valuation than many founders could find elsewhere, you could consider the equity the price for access to the YC network and existing companies to use your product.