Hi M3tav0X, that is a valid concern! I'm with you there that Pedro's story should be able to have a happy ending regardless of the nature of his and Oscar's relationship, so worry not. Seconding what Minoanon said, you will still be able to get Pedro to join the hotel after chapter 18 even if he and Storm don't end up in a romantic relationship. Spending time together during Hinterlands III is one of the factors that nudges him in that direction but it's not the only one, your performance in the other quests also has an effect on this.
In fact Pedro joining instead of Nikos will be the most likely outcome (I expect most players to not have Nikos join on their first playthrough since the method to get him is a lot more complicated).