From a technical point of view, you can easily consume another webservice (B)
from within a webservice (A). No problems with that.
However - from a design perspective it does raise questions. One of the
socalled tenets of SOA indicates that a service (A) should NOT be dependent
on other services (B); but it really depends on what purpose this "other"
service (B) serves.
What to think about? Well - authentication towards the other service (B)
from (A) is an issue you should consider. How would you authenticate the
caller (A) to the service (B)? Should impersonation be used to impersonate
the calling person, calling A and then impersonate him to B? Several options
exists for authentication, but these issues are (and should!) be present and
considered in any SOA architecture.