There are no known interactions with blood pressure medication (including losartan and atenolol) and beta-hydroxybutyrate. However, there have been no studies testing for interactions so we just might not have enough data.
Beta-hydroxybutyrate, a naturally occurring endogenous compound, is relatively new to the supplement scene. It is a ketone that is used as an energy alternative to carbohydrates and is purported to "trick" the body into thinking it is in ketosis, with the hope that fat metabolism will increase.
There are no well designed studies of beta-hydroxybutyrate in humans. There are a few small ones in rodents, but the complete effects, especially on blood pressure, aren't well known.
It should be noted that there have been several studies that point to the fact that low carbohydrate diets can lower blood pressure. As beta-hydroxybutyrate is typically used to lower carbohydrate intake and utilization, there may be a small possibility that it can lower blood pressure over time, but again we don't know for sure.
Overall, it seems like the risk of an interaction with blood pressure medication is low, but you should still make sure you doctor is aware of all the medication and supplements you are taking so you can be appropriately monitored.