Generally speaking, yes. You can run into issues if you try to run a set on a smaller diameter circle of track than what it came with, but since most starter set trains are designed to handle small diameters, the problem is rare.
You shouldn't as long as they are the same code. You could even overcome that obstical, but I guess I gotta ask, why would you want to mix the two in the first place?
I am not really wanting to mix them but the hobby shop here sells the starter sets but they come with e-ztrack and if i bought one would the loco work on regular track
I've seen E-Z track mated with Atlas (both were code 100...) and as long as you "shim" under the Atlas with cork or foam roadbed, and bring them to the same elevation, you'll be fine.
I am not really wanting to mix them but the hobby shop here sells the starter sets but they come with e-ztrack and if i bought one would the loco work on regular track