Any legit way to use a full feed from a celebrity type site or news type site?

I see tons of blogs that use popular feeds and have the adsense or cpa ads incorporated.

Is there any worry for those doing this?

Is this okay to do, and if so what are the things that needed to be done to be on the right side of the line.

I am asking because I have a guy wanting me to build a site like this and want to make sure that he will be okay.

Thanks

I think that I will pass on building his celebrity site... Seems no response means it must be Total Taboo.

Yes you can.
You should contact the owners of the feed and simply ask for their permission.
Simply make clear that it benefits him as well as you by providing him backlinks as well as traffic through those backlinks.
Make sure you include a link to the original source.