So my friend find out there are two ways to make Houdini Engine works in runtime. His is very shy so I will post his finding here for him. Hopefully SideFx will look into this and make Houdini Engine in runtime available soon in the future.

You can view his evernote here however it is all in Chinese
https://www.evernote.com/l/AFzcxO01IBtK47eWdNtDLPo13w05peBvdK0 [evernote.com]

The first way is to load Houdini Engine in your code. You can look at his example in the attachment.

The second way:

1. Change the unity build setting Architecture (below target platform) in to Universal
2. Make a copy of libHARC.dylib inside houdini library folder, and rename it as libHARC32


Try it yourself and if you have any question just ask away!