No, the Apache envvars file is considered a configuration file, and MacPorts does not typically modify your configuration files for you.
Are you certain your ports are up to date? ("sudo port selfupdate" and "sudo port upgrade outdated") It was my understanding that with the current version of the port on OS X 10.5 and later it should no longer be necessary to do that, which is why on 10.5 and later the notes of the oracle-instantclient port currently read:
$ port notes oracle-instantclient
oracle-instantclient has the following notes:
If you previously set DYLD_LIBRARY_PATH=/opt/local/lib/oracle in your environment, you can remove it; it is no longer needed with this version of oracle-instantclient.