Nevermind! Figured it out! For those of you trying to figure this out here is what you do.
In the project directory create a plugins folder and then drop the plugin directory in there. In my case it looks like this…
MYPROJECT → Plugins → HoudiniNiagara
Unreal will find this automatically so you can turn it on in the plugins window. Weird thing is you have to search for it, but it is there.
Only issue I’m having now is that I’m having trouble getting the new project file settings with the new plugin turned on to push to the perforce server so that it is turned on by default for all users. Any help is appreciated!!!