Yep, @jeff guesses right. The expander board supports all of the common ws281x chipsets and clones that operate at the 800KHz data rate. These are mostly compatible with a few variations, and Pixelblaze and the Output Expander use timing that are broadly compatible. Even 12V LEDs use 5v data signaling.
Keep 12v separate, and feed 5v for Pixelblaze + output expander. The GND (or negative) will be shared across both.
@BanhammersWrath made a pretty sweet 3d printable case that might be inspiring, but it didn’t have IP67 in mind. You might find it useful as a reference though.