It's hard to tell who does. I know most of the witnesses personally but sometimes am surprised. The best indication is looking at who is online and waiting during chain halts and hardforks. Those online are working on their servers or waiting for information. Those who are not are not because they don't need to; someone else will take care of it for them. Combined with that is also giving some consideration who is trying a new version (right after our hardfork there were numerous versions out) or who has different witness-set parameters in some way. If someone is just running one hands-off and doesn't quite care for working with the technology or understand it they will go the simplest route provided for them by the operator and never try anything new. All of this doesn't make someone a bad witness because they may have a highly-skilled operator. The server is still properly run and can sign blocks.
Not running own is sometimes the right choice. I remember there was a witness on Steem who was relatively well-voted but ran his node from an old laptop in his basement that kept having hardware issues. The name escapes me. Anything would've been a better alternative.
It comes down to caring about the blockchain over own wallet. Is the person doing everything, directly or indirectly, to run it properly? Good. Is the person just milking it with the shittiest hardware that can even sign a block? Bad.