Hi Abby! What is it that you'd like staff to self-assess? Basics of engaging volunteers or going deeper? Basing it on the concepts in the volunteer management cycle or more transformative?
This may or may not be helpful, but VolunteerPro recently shared some resources on self-assessment (scroll down to Self-Assessment & Team Culture Tools for Volunteer Program Development). I bet you could riff off of the Impact Culture Checklist (PDF) a bit. Reading over the statements I could imagine replacing words to make it more relevant to volunteer engagement.
If you want to brainstorm over a video meeting, let me know! I'd be happy to help bounce some ideas around. =)