I've tried googling but can't find anything. The idea here being that instead of having to open up a .blend file in Blender, export it to say FBX/OBJ, and then add a FBX/OBJ import node, one could instead just have a "Blender Import Node", and give it the export parameters in Houdini, and it would then run the Blender export in the background.

Unity used to have something like this (https://docs.unity3d.com/560/Documentation/Manual/HOWTO-ImportObjectBlender.html), although it was removed because it lead to issues when people would share .blend files and have different versions of Blender installed, though that to me seems like just an implementation issue (e.g. no version check/pinning).

I wonder if anyone tried to do this or have any tips? The main thing I want to avoid is just the extra round trip and having to open blender, choose an export path, then choose the same path in Houdini and import, it'd be really nice if this could be done by just pointing Houdini at the .blend file.

There are two ways that should be simple to integrate.

1. Commandline : https://docs.blender.org/manual/en/latest/advanced/command_line/index.html [docs.blender.org]
   
2. Python Module : https://docs.blender.org/api/current/info_advanced_blender_as_bpy.html [docs.blender.org]
   
3. HAPI(not ideal for your case): https://www.sidefx.com/docs/houdini/hapi/ [www.sidefx.com]
   

It looks like Commandline is very simple to use.
https://blenderartists.org/t/how-to-export-mesh-object-to-fbx-from-command-line/1144571 [blenderartists.org]

To just convert a .blend to fbx-obj you should be able to use Houdini to generate a Python snippet file then launch Blender with it (without GUI). Then you get your files.