Mekanism 8.1.5
Railcraft 9.6.1.0

Although the cables don't connect, and energy doesn't flow into the cable network - all the energy seems to be flowing . Into oblivion.

It does however, work when the engine is directly adjacent to a machine. (And not feeding into a universal cable.)

Is there any chance of this being merged into the main branch?

The issue here is due to Railcraft engines only implementing IEnergyConnection, rather than IEnergyProvider. Worked around in dev branch d994f18