Which statements of Zimmerman are you referring to?
FWIW, I don't think any of his statements would be struck as self-serving. His recorded marks before the physical altercation can't be statements of self-interest, in the meaning of the Williamson case.
His (or any potential suspect’s) statement that the guy he shot attacked him would be considered self-serving unless it were to be corroborated by a neutral witness or evidence such as a condo-complex security camera. That’s just the way the law works.