The 1U system I had, the heatsinks have been fanless and not the extruded aluminum block one usually thinks of, but an assembled stack of much thinner, more rigid fins. It relied on airflow from fans mounted in the middle of the case, between the mobo and disks, shrouded to focus that airflow. I want to say 2x40mm fans per processor.
You should expect a 1U system to run hotter than a desktop, and definitely hotter than cooler advertisers want. CPUs are designed to operate up to 100°C or so, and the constraints that lead people to use 1U form factors generally include replacing those systems regularly, basically because of burnout.