If you want separate widgets for separate services that's simple to do, you can add as many different widgets for different services as you like (although you may see performance issues past a certain point).
If you want multiple datasets to be accessed by a single widget, you can use Data Expressions. Data Expressions let you create kind of a 'virtual' layer or table in whatever way you like, for example calculating statistics or deriving new fields, and it's also possible to use them to query multiple services and combine those records into a single feature set, and have all the results combined together in a table, indicator, chart, etc.
