nope I wouldn't do that.
Check this out. I'm going to do something like THIS.
A center piece should be something you're proud of, not something you just throw together.
The thing in the YT video is gorgeous. I'm inspired to build something even better, but the only problem with the one in the video is it's probably not safe for betta fins.
I'll have to figure out a different stone to use.
I would cover the rest of your ExoT cave with pool filter sand instead or with diamonds & pearls.