New hardwood floors and steam radiators

Question is a bit vague, but I'll take a shot. If I was doing the work, the radiator should be disconnected at the valve so the new hardwood flooring can be laid across the entire floor. After the new flooring is done, move the radiator back into position and reconnect.

A few things to be aware of, you need a bit of slop in the feed pipe to make this work as the radiator will sit a bit higher than original (depends on new flooring thickness). I've done this in my house without issue, but not all piping has the necessary slop to make it work. If you don't have it things get more complicated and may require some creativity with fittings and possibly moving the radiator (in the length) to make room for the extra fittings. I wouldn't expect a flooring contractor to do this.

Since you are hiring someone to do the work, I am curious what you have agreed upon. Details like this should absolutely be in the contract for the work being performed.

If they plan on cutting the new floor around the radiator feet, I can't think of any way that can be made to look good, but I have seen it done.

No matter what they decide to do, make sure the radiator has a slight slope towards the inlet valve for proper drainage.