I am certain drugs to be recommended for pregnant and nursing mothers are thoroughly assessed before they are prescribed. If the benefits outweigh the likely negative effects, that goes the green. If otherwise, then it would be a no-no. Sometimes, medical experts just have to recommend the best of many evils.
Having said that, I am certain that most hypertension drugs are generally safe for babies as only trace amounts are known to get to the lactating channels. I am optimistic that your baby would be fine. Thanks for the insightful contribution.