When network is down, shareplex will stop some process. when network is up, shareplex will restart that process again. Since it only read the log file, it will have less performance impact on production database. While oracle use internal triggers to do replication, it do slow down production database.
Why do you need replication? If one of your database is readonly, then, use standby database. I was told in oracle 9i, standby database can open for read and under recover mode at same time, although I never set it up myself. I am still using oracle 8i.

xyz2000