The Gunners loanee has scored six goals in eight Bundesliga appearances and picked up the league's rookie of the month award for October.
It is unclear whether Arsenal will recall the 18-year-old, but nonetheless, Emery is ecstatic about his progress.
"Firstly, we are happy when one player is leaving to play [on loan], take responsibility, take rhythm and take a high level like Reiss Nelson in Hoffenheim," Emery said.
"We are following him and his performances, his good performances, and also his playing minutes.
"For us, it's very important to follow him and his performances that he's giving.
"His progress has been great. In pre-season he worked with us but here minutes and responsibilities are more difficult because he's young and the decision to leave is important for him and for us.
"I think at the moment he's progressing how we want."