Currently under the PPACA you cannot be denied insurance for prexisting conditions, and it is reasonable to expect pegging UBI to just poverty + cost of bronze single person plan in your area rather than implementing universal healthcare.

Not trying to argue it isn't cheaper to cut out the insane middle men in the healthcare industry, or that the current insurance system works at all (deductibles cost society incredible amounts of money and time because people won't go to the doctor until they are dying because of the unsubsidized costs) but if your goal is to have everyone insured, fed, and sheltered you can do that with just the cash payments while just enduring a disastrously inefficient and harmful healthcare system besides it.