That's not how security works. FreeBSD has more exposure than OpenBSD, but OpenBSD is more secure. Security isn't a measure of how many people have heard of your project, it is a question of whether or not you have carefully designed your project to be secure. Haskell helps prevent a ton of errors that can cause security holes. On top of that, yesod at least has been very carefully designed to both be secure itself, and to make applications developed in yesod be secure by default.
Security holes don't just magically go away when software gets popular. You should be striving to not create security holes in the first place.