I try to set a fluid as the the input but getting:
// Error: file: FProgram Files/Side Effects Software/Houdini 15.0.393/engine/maya/maya2014/scripts/AEhoudiniAssetTemplate.mel line 628: Selection has no supported object that can be used for input. //

If I do the same thing for a poly object it works as usual.

The Maya plugin doesn't support inputting fluid/volumes yet. It's definitely on my list of to-dos. Out of curiosity, how do you plan to use input fluids?

It's possible to output Houdini volumes back into Maya though.

Aha, I misread the sticky. Didn't see it was only available as Output.

I've got a request from an artist on converting fluid velocities to image data. This to generate a flow map in a game.

I was thinking maybe you can convert fluid into particles, and input particles into Houdini Engine. Particles can only seem to read the fluid's velocity data easily. However, there doesn't seem to be an easy way for particles to read the density and other grids.

If you only need velocity, then this workaround might be possible.

That's exactly what I said. Turns out there was a script (https://www.youtube.com/watch?v=BwuDtaoWaSw). [youtube.com] It looks rather clumsy against a Houdini solution but I get why volumetrics inputs isn't the highest priority.