Not outright plants, but a lot of people in the industry are friends with a lot of other people in the industry, so to some extent it's inevitable that some business dealings will be porous. For real high level stuff, dramatically less so. The studio leads at Bethesda didn't seem to know what was happening until it was announced.
For SE, I don't think it's highly likely that a sale will happen. But the previous reporting denied by SE (or denied in very specific language, anyway) about companies being interested is something I find highly plausible. The games industry has been on such a hot streak the 18 months that it's inevitable that people are sniffing around at most every company, regardless of whether the companies themselves have any intention of accepting plausible offers.