I saw that Korean students say 수고하셨습니다 to their professor in Korean movie. So you can. But technically 수고하셨습니다 or 수고하셨어요 doesn't mean "thank you". And you need to be careful when you say it. This is what my friend told me: You can say it when someone gave you a great help. Such as when your neighborhood repaired your broken shelf or your computer. BUT you need to say "감사합니다/고맙습니다" as well OR serve them a juice or something with a big smile. I'm still not sure about this. So I just don't use it. However I saw some cases Koreans say 수고하셨습니다 or 수고하셨어요 in online it's like the Yahoo Answers when they translated the whole English sentences into Korean for them. But they're crying LOL. They said something like this: 헐 ㅠㅠ 진짜 수고하셨어요 ㅠㅠ 진짜 감사해요 ㅠㅠㅠㅠ (OMG thank you for the great job you did TT Thank you so much TT). You can say thank you in different versions and also you can say the same thing differently. You can use 해요체 or 합니다체 like this: 답변 감사해요(or 답변 감사합니다), 친절한 답변 감사해요(친절한 답변 감사합니다), 덕분에 많은 도움이 됐어요(덕분에 많은 도움이 됐습니다).

Yes, you can. You can say "수고하셨습니다" or "고맙습니다" \^o^/