Can I use this for bare spots in my existing/well established zoysia grass? And does it blend well with Zoysia?

You could try it, it's dark green, I'm not familiar with what different grass types look like. Accept bermuda grass.

No. It will compete with Zoysia. Best to use Rye grass till the Zoysia fills in.

I tried to overseed with my z grass.would not come up

It certainly will grow within your existing zoysia grass, but I would not recommend doing so. Zoysia grass is a warm season grass that should be cut low, and fertiized in the summer. All the seed varieties in this mix (tall fescue, bluegrass, red fescue, chewing fescue) are cold season grasses that should be cut relatively high (2.5 - 4 inches) and should be fertilized in the spring and fall. Also, cold season grasses stay green throughout the fall, winter and spring, while zoysia grass goes into dormancy and turns brown when daytime high temperatures fall below 70 degrees.