This depends a little bit on the situation, but since the ADM service only services background processes it is generally fine to have only a single pod. If the cheapest option for you is to size up the single node, then it sounds like a good solution.
One thing to maybe keep in mind though if you target only a single (larger) node, if the load increases in the future and the system scales to two pods you might now be over provisioned again. When having multiple smaller pods, the step increase of adding an additional pod is smaller.
Lastly, if it is scaling back down immediately it can also help to set or increase the sabilization window for scaling down: Horizontal Pod Autoscaling | Kubernetes