A-I have seen them beaten up.
This sentence can mean:
1-I have seen them get beaten up. ie. the process of their getting beaten up
but can it also mean
2-I have seen them after they had been beaten up. ie. I have seen them in a "beaten up state".
I would read "I have seen them beaten up" as meaning "I watched as they were getting beaten up". Other meanings might become apparent with additional context.
The first is the natural assumption, but the second is a possible meaning.