Surtur will not be under Loki's mind control.
The army of the dead whom Hela resurrected were her loyal allies from her past and were under her control before their death. Fenris wolf, the loyal pet of Hela was also brought to life along with them.
It is clear from her dialogues and the pictures on the ceilings before she resurrects them. We can see the pictures of the army who were under the control of Hela and supported her.
Hela: Before that, Asgard's warriors were on it. Their bodies buried as heroes beneath this very pass.
Hela: My God! what they have done to you?....
With the eternal flame, you are reborn.
Hela: I missed you. I missed you all.
Surtur is neither a loyal person to Loki in anyway nor a friend to him. So, he would not be under the control of Loki.