It’s best to keep hiring the same artist. Things like line quality, color palette, shape palette can be created. Placement and scale relationships and ensuring that the work is only handled by those who have some art training and ability. One might have the artist come and audit / critique strong vs weak executions with reasoning as to why. It helps with onboarding too to have a check in as a new person may not integrate undocumented nuances. Or they might evolve the system in a way that the artist finds is an improvement vs one that the team already ruled out.
I carry errors and omissions insurance at the time of writing as it was a client requirement. I'm not a lawyer, so I won't claim to know all compliance requirements, and I'd push back on the idea that any artist should be expected to walk in as a compliance expert for a specific organization before being hired, that's not a reasonable bar to set. What I can say is that I'm familiar with the environment, having worked inside it, which is different from claiming unlimited legal knowledge. If there's required reading like extensive internal documents or policies I'm glad to be paid to go through them properly.
To answer more generally: You can see the clients in their portfolio. The more experience they have the more familiar they might be. Even if an artist has a solid legal understanding there may be preferences and nuances your organization chooses to weight in a certain way. So a better question could be how might we develop training so you can ensure the artist is equipped to understand your specific context. Ai can be helpful at making this. Others also have errors and omissions coverage, but your own organization presumably has this for itself and it may already cover contractors. Either way it's good to ensure your own processes are designed to catch and resolve any potential errors or misconceptions in this area.
On NDA specifically: it's reasonable to keep drafts, exploratory concepts, or placeholder ('FPO') copy confidential; those aren't meant for public view. But once work is approved and made public by the client, portfolio rights to display it (with proper crediting) is a fair expectation, not a risk to the client it's clearly a piece of past work in an artist's portfolio, not a live communication from the bank, and any offer shown may no longer be active. A simple disclaimer line can address any residual concern.
It's also worth considering as a form of earned media: when an artist shows the work to their own audience, that's free additional exposure for the brand, at no cost to the client. The same logic applies to recruiting — many organizations showcase their design team's work on their own corporate site, crediting everyone involved, because a visible portfolio is part of what attracts talent. Restricting an artist's ability to show approved, public work, without a specific, articulable risk, cuts against that same interest. Worth clarifying portfolio usage rights in the contract up front, rather than leaving it ambiguous.