No they wouldn't be considered lawful combatants even if they were Ukranian's repairing it. Unless of course it was some kind of military engineer corps. I'm not gonna act like I understand the intricacies of international law so I'll post the definition and source from an article.

According to the Third Geneva Convention, combatants are: members of the armed forces of a party to the conflict, as well as members of militias or volunteer corps forming part of such armed forces (GCIII Art. 4.a.1); or members of regular armed forces, even those that profess allegiance to a government or authority not recognized by the adverse power (GCIII Art. 4.a.3); or members of other militias and members of volunteer corps, including those of organized resistance movements belonging to a party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that such militias or volunteer corps, including such organized resistance movements, fulfill the following conditions: that of being commanded by a person responsible for his subordinates; that of having a fixed distinctive sign recognizable at a distance; that of carrying arms openly; that of conducting their operations in accordance with the laws and customs of war (GCIII Art. 4.a.2); inhabitants of a non-occupied territory, who on the approach of the enemy spontaneously take up arms to resist the invading forces, without having had time to form themselves into regular armed units, provided they carry arms openly and respect the laws and customs of war (GCIII Art. 4.a.6).

https://guide-humanitarian-law.org/content/article/3/combatants/#:~:text=Combatants%20are%20under%20the%20obligation,acts%20are%20considered%20war%20crimes.