Seam injection isn't the simplistic creation-time configuration like other IOC frameworks. Seam injection happens at invocation time. Instead of thinking of injection, it might be easier to think of it as a link to contextual to state the Seam keeps current.
So then my objects that are at the class level are safe then??
Is it the same for outjection as well?
Injection and outjection occur at every invocation. If you change an outjected value during an invocation, the change will be outjected to the appropriate context after the invocation.
So... Yes, injected objects are "safe" in a SLSB because they are injected at the beginning of each invocation. (and they are actually disinjected after the request, so there is no leakage)