Under the UN rules, conflicting parties do not participate at all peacekeeping operations. Neither Ukrainian, nor Russian representatives should be part of a peacekeeping mission. This is a general rule for the formation of peacekeeping missions.
There are various algorithms for peacekeeping missions. They can be divided into coercion for peace and peacekeeping. These are two completely different missions. If it is compulsion for peace, it is necessary to force to peace not a victim country, but a country aggressor. But even in this case, the representatives of the conflicting parties are not included in such missions. This is a UN rule.
If we are talking about a peacekeeping mission, then the Ukrainian side may be involved in the temporary territorial administrations. The forces for demining can be attracted, where they are not connected with the resolution of the conflict. When it comes to the elimination of the consequences of the conflict, they may be attracted. They will not play a key role there. And in the resolution of the conflict, the conflicting parties do not participate, otherwise the mission ceases to be neutral, and this is the first UN rule.