Try it. You can sign up for a free developer org. Change a fields permission in the profile to read only. Then create a workflow rule that updates the field. Login to your org with a user you have created using that profile and you'll see if it updates or not.
I just came across this answer while looking for the same thing mysellf.
But, it is wrong.
I don't know if this has chnaged in SF since 2014, but currently (May 2022):
Field updates function independently of field-level security. Therefore, a workflow rule can update fields even though they are hidden on the user's page layout.
You cannot update a field through workflow which is readonly on your profile.
Please mark this as best answer if it helps!
Thanks
Grazitti Team
All Answers
You cannot update a field through workflow which is readonly on your profile.
Please mark this as best answer if it helps!
Thanks
Grazitti Team
I just came across this answer while looking for the same thing mysellf.
But, it is wrong.
I don't know if this has chnaged in SF since 2014, but currently (May 2022):
Field updates function independently of field-level security. Therefore, a workflow rule can update fields even though they are hidden on the user's page layout.
https://help.salesforce.com/s/articleView?id=sf.workflow_field_update_considerations.htm&type=5