I have them open up their CRM tool of choice. Then I have them explain their funnel. They should be able to step me through how they've setup their stages: Qualifications, Needs Analysis, Decision Makers, Value Proposition, Quote, Negotiation, etc.
Then I have them deep dive on a particular deal and have them explain each of these stages for this particular deal.
If you want to see them "code" get them to sell to you. Do they ask good questions? Can they relate answers you've given to an actual proposition? Are they so thorough and accurate they've ended up with a watertight business case for that proposition? Have they identified other hypothetical stakeholders they're going to need to ask similar questions to present similar cases to, and how far you'll help them with that? How do they respond to your 11th hour attempt to reduce the price? That's "coding". The other stuff is architecture: important but pretty useless without the fundamentals unless you're looking for a pointy haired guy.
Plus the really good sales guys often intuitively breeze through a lot of those official "stages" in one call or meeting, whilst appearing "stuck" at another stage for ages, and are completely comfortable with that because they know what aspects of the sales cycle they can and can't control, and why they'll be waiting. This probably sounds less impressive than the textbook example of steady progress a good bullshitter should be able to come up with.
(1)arguably worse: probably the best explanations of pipeline organization you'll hear are from underperformers in large companies who have to explain their activity to their line manager in more regular review meetings. The guy that sucks at writing code probably gets less regular invitations to meetings to decide on application architecture.
Even ignoring the ethics of the request, if somebody is willing to act against their current employer's wishes, they're almost certainly going to act against my wishes as well.
There are plenty of ways to check an applicant's abilities without requesting access to confidential information. This is as true for biz dev as it is for coders.
As such, I think it's a poor idea to make that a standard part of the interview process.
You mounted an unwarranted defense. There are edge conditions where somebody could do so without a problem, but they're the exception that proves the rule.