I know RIM is hoping to have their cake and eat it, too, by thinking that if they associate their name with Android, then a lot of developers will come to RIM. First of all, that still makes little sense because even if many developers came to RIM, they could come for the Android apps, and wouldn't be interested in learning RIM's new SDK's and other development tools, for another OS that might never past a few percentages of the market.
Second, I really don't think that many Android developers will even bother to repackage their apps for RIM's Playbook OS. There are almost 500,000 apps on the Android Market by now. Maybe a few thousands at best will be ported to RIM's custom Dalvik VM, which pretty much makes "Android apps on Playbook" a gimmick. Add to this the latest news that those apps won't even support mobile advertising, so developers can't monetize their free apps, and the fact that it's a gimmick is guaranteed.
RIM is still willing to go all-in with the company and bank on the Playbook OS, even though the chances for success a very low. RIM has already lost 80% of the market share they had in US in 2009, down from 44% to around 10% now, and dropping fast. They have quickly become a small player in the mobile market, and having their own OS with its own apps that nobody cares about, is only going to make this worse.
If they were part of Android, at least they would have the huge ecosystem behind them, even if they wouldn't be able to compete very well with Samsung and the others. Not to mention that RIM isn't even that good at making software. So now they are left not only with hardware that is at least one generation behind everyone else, but also with software that lacked even a native e-mail app in version 1.0, and many other features as well. If RIM were serious about Android, they would just join it already.