I've been doing a lot of experimentation with my photos workflow over the past couple of months. Apple Photos is great as it gives me the ability to have all my photos on all my devices and seamlessly integrate with apps on my apple hardware. That said it lacks a lot of the processing features that I need. Additionally I've started really getting into RAW shooting and wanted an app that could do the developing and processing of the raw files. For me Lightroom CC is filling that niche nicely. I wanted the two apps to work together but there is no way to directly share from Lightroom to Photos without doing an export to the desktop and then dragging into photos. With some trickery using hazel, I've been able to create a workaround for this.
The first step is to create a new folder somewhere on your mac called Lightroom Export or something you'll remember later. I've located mine in the Pictures folder of my user account. Next is to go in to Hazel and set up that folder as one of the "watched" folders. Then create a new rule:
Once this rule is created click Ok and go back to Lightroom. Lightroom allows you to create preset export path's that can be configured and re-used. If you go to file and export it will bring up this menu. You can create a new user preset on the left and then set the conditions. I set the export location to the new folder you just created for Lightroom Export. You can set other conditions such as renaming, adding a watermark and adjusting the size etc. For me I'm changing the file name and selecting the export folder. Once that's done and you've saved it as a user preset.
From your filmstrip or library you can right click, select export and select the user preset you created. Once the export is complete, you'll notice that hazel takes over and you should get a notification that a file has been added to Photos and that the file has been moved to the trash (if you have notifications turned on). Simple as that. Hopefully in El Cap there will be more plugins available for this type of inport to Photos, but for now this is working just fine for me.
As to my workflow, I'm doing all my RAW processing in Lightroom. From my SD card the photos go into lightroom, are processed and adjusted, and the finished copies go out to Apple Photos.