Hmm, I am not sure about how to make a slice with a near and far planes in Octane. Anyway yes, the deep rendering must be enabled in the kernel node to be computed, and in the ROP node to write the file. Perhaps you could play with the kernel max. depth samples and depth tolerance parameters to see if this can help with the memory issues.
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini