I'm a fan of allowing the player to see where the boss is, as in other roguelikes like Returnal, because it allows the player a choice: push on now or try and power up before facing a boss. There's still a chance of it being a non-choice, as when a player is struggling and therefore must take extra time to power-up or when an advanced or impatient player is in a rush and so must face the boss as soon as possible. However, taking the choice away removes control for the struggling player, the advanced player, and for all other forms of player. It makes the game a bit less interesting and a bit more tedious.
If ambush bosses are part of your design intention for the game that's fine. I feel like it's a missed opportunity though, especially with shops also being hidden to the extent I've yet to see them.