It will grow but not fill in because it replacates by rooting stolons so remove the weed barrier and use mulch, bark preferably, to keep the weeds down and even if they grow they will be easily removed.

Here is a link that might be useful: Propagating Perennials

You think it'll work if I score the heck out of the weed barrier between and around the plants with a box cutter aka carpet knife? There are areas where there are still very strong weed roots that I couldn't get out (next to the neighbor's concrete edging.) I'm thinking leave the barrier intact just along that edge and score the heck out of the rest, covering it with mulch too.

Erg.

Here's my weed strip before I put down the weed barrier and planted the ajuga:

Just a warning about that fabric. Weeds will make their way through it. And then you can't pull them because they get stuck in the fabric. Poison ivy, raspberry, virginia creeper are especially tough to get at through this fabric. Your area isn't very large so you can probably stay on top of it. I think if you slash the fabric you will be defeating the purpose. You could use ten sheets of newspaper under mulch. That will kill what's there, but will biodegrade. And you can replace it whenever you put on more mulch.

I have an area 12-15 feet deep by 200 feet wide, installed by a previous owner. The area was neglected and I'm slowly restoring it. Just to add to the fun, red stones cover the fabric in between blue rug juniper and myrtle, instead of mulch. And it's a slope, so at the bottom of the slope there are over 8 inches of stones that have washed down.