Interesting, I have a history in West Coast food co-ops as a baker, manager, and volunteer board member. In my time of direct involvement (1997-2007) I didn't see any union busting or undue influence from UNFI, CDS or other outside entities. Of course it's been a while since then!
Additionally, I found the Carver Policy Governance model we followed effective and intriguing. FWIW "speak in one voice" on our board was a strength, meaning we worked out our differences of opinion on official matters in the board room, but were always free to voice our independent opinions as member-owners and expected to make it clear which "hat" we wore (board member vs. member-owner) when talking to members.
My quick gloss on Policy Governance - Basically you draft "Ends" that the organization follows (mission & values, etc.) and then prohibit what means the GM can take to enact them. Everything else is up to them, and if you're doing it right as a board you're paying VERY close attention to language and intentions, and chains of cause and effect (always keeping "bad GM" scenarios top of mind). The board is basically the legislature (and judiciary in times of need) to the GM's executive branch.
Maybe it's unique to the co-op I worked in - but a key part of being a board member was "Member Linkage" meaning that while the board couldn't directly enact the changes that members requested, it was 1000% our obligation to listen to them, give them space on agendas, and take these requests seriously. When I was involved, employees were encouraged to run for board seats, and AFAIK there has always been direct staff representation on the board before and after my tenure.
IANAL - But if a board member knowingly lets an outside entity change its bylaws in a way that negatively affects the co-op and its members - that is a breach of a board member's fiduciary duty for which they could be personally liable. Same - if an outside corporate stooge is installed on the board and prioritizes their outside biz' well-being over the co-op's, that would also be a breach of fiduciary duty. Also - if such a stooge ran for a board position and didn't disclose their business connection and intention to prioritize their employer's needs over the co-op's, that would be a blatantly clear conflict of interest that is grounds for immediate removal in any org with decent bylaws.
So - not calling BS on this, but something isn't quite adding up here in the articles linked.