If you have not already seen this page, here is the Nintex Automation Cloud Limits documentation: Limits (nintex.com)

I do not see any mentions of a limitation for the number of people you can add to the control.

Yes I checked and didn’t see it but good to know I’m not the only one that couldn’t find anything.

@brandiwoodson 

I think limits for people picker are higher than you may ever need, Typically values entered into the people picker will be filtered by what you enter, for example typing in Jane will then perform a query to return all accounts matching ‘Jane’

I am not sure if there is a limit on the number of ‘Jane' records you can return say you have 10k Janes, I think it is likely to be somewhere around 1000-5000 records at a time as this is typical for a Microsoft API call but at that point typing the last name should really further reduce the options below 1000-5000 dropdown limit.

however there is no limit to the number of accounts the people picker has access to AFAIK.