The incremental backup from SCN is a 10g feature.
From my point of view, you have 4 possible scenarios:
Scenario 1 - Regular Database with old archive logs
In this scenario you can restore the archives to the right location, then issue a recover operation using RMAN (connected to the standby database) and then start the standby recovery process
Scenario 2 - Regular Database without old archive logs
In this case, the faster bet is making a disaster recovery operation to "duplicate" the database.
Scenario 3 - Massive Database
In the case that you're working with a multi-terabyte database, you have to check what will take longer, getting the old logs (if any are available) to recover the standby or creating a "new" standby database.