If your organization employs freelancers, it must consider the risks involved. Certainly, the risks related to a graphic designer are lower than that of a freelance data engineer who may be altering code or accessing your data. Many individual graphic designers don't carry professional insurance due to the fairly low-risk nature of the work.
In my experience, I don't feel proof of insurance for a graphic design freelancer is necessary so long as your contract is clear regarding the responsibilities of both parties. Should you decide to request proof of insurance for that Freelancer, ensure, you have documented insurance requirements for all freelancers and contractors to avoid any perception of unfair business practices or barriers to work. I hope that is helpful, but I would also like to hear what other members think.