Acculips looks pretty precise within iClone, but when I render an .fbx to Unreal, the visemes and lips curls vanish, leaving me with a moving jaw that simply flaps up and down.  Is there an export command I'm missing, or is this something I need to fix by keying in visemes?  I was hoping that acculips did that for me on the export.

Have you tried Unreal’s own facial live link tool?  They just did an update about 2 weeks ago which finally lets you auto adjust to a neutral face pose just by clicking a button. It’s not as accurate as what I’ve seen people can do with Faceware but it’s pretty good and very easy to get working.  Hope this helps.

Sounds like you didn't tick "import morph targets"in the UE4/5 FBX import settings.
IClone exports morphs by default.