Yes, there's a little room before immigration, but very limited space. It's not somewhere you want to linger for long. Don't think there are many seats at that Starbucks, if any. And unless there's some serious issue with the documents, otherwise HK Immigration officers do not like to open their mouths. Your friend should not have issue going through immigration there.

But it's your choice. If you insist in waiting, then you can, mostly likely standing. All arriving passengers will arrive at that single point before diverging to the two immigration lines.