Yes there is a risk of this. But, with modern tooling, you don't need to do this to accomplish the same goals. It's not hard to figure out the high level approach of what someone else is doing. It's not hard to figure out a significant number of their customers. There are entire companies that exist to answer these questions for you. Ultimately, if you're looking to sell your company, you will have to trust the acquirer. This isn't a GitLab thing, it's just the name of the game. I wrote a bit about selling my company a year ago [1] and it was similar, except a lot of the diligence happened post LOI / Term Sheet. In hindsight, I kind of wish it had happened earlier.
[1] https://www.nothingeasyaboutthis.com/lessons-from-selling-a-...