Google's Inbox email client is still in somewhat of a limited run, as it's not yet open to all users and you still need an invite to access it. Google's efforts to bring it mainstream seem to be chugging right along though and as part of their current strategies Inbox will be on its way to including Google Apps accounts for Inbox compatibility. Google's head of Android and Chrome Sundar Pichai already outed last month that Inbox by Gmail would be coming to Google Apps accounts in the near future, but had failed to mention a definitive timeframe or an exact time rather. It would appear that some Google Apps accounts are already starting to receive the ability to use their work Gmail accounts with Inbox though, as noted by Android Police.
Not too long after Pichai had mentioned Inbox would be making its way to Google Apps accounts, accounts administrators were able to show interest in receiving invites to use the app. Google hasn't officially announced that Google Apps accounts are now receiving invites, but the team at Android Police seems to be among a limited round of administrators who are already able to merge their work Gmail accounts into the application. Does this mean Google is going to start ramping up the adoption rate of other Google Apps accounts? Possibly. However, Google is likely to keep the access to a small set of accounts for now as they won't roll things out on a wider basis until things are completely ready.
Account administrators can still apply and show interest in receiving access so if your team or company is not yet able to use Inbox with your Google Apps account, the support page that Google has created for this scenario gives the rundown on how to potentially get things working. This of course, is all up to Google's discretion, so showing interest doesn't mean you'll end up getting access even if you already have Inbox set up with your personal Gmail account. For now there is still no idea of when to expect Google to officially roll Inbox out for Google Apps, but perhaps this signals that things are closer than we think.