Understanding what resources UDT requires and uses is an interesting challenge.
Check out these two links for information about how many UDT devices can be monitored by a single UDT poller.
The first document linked shows the Primary Poller Limit is 100 K ports. And every APE can each manage 100K additional ports. The limitation is 500K UDT Ports per instance (1 main poller and 4 APE’s). My environment is identical to this, although I’m not clear whether all UDT polling is occurring from only the main instance, or from it and all APE’s.