If the two applications share the same data (I mean really the same data, same schema, same tables, not just the same database server process), then they need to be synchronized when updating the shared data. You mention row locks. Those need to be present, whether you cluster the database or not. However those locks are fine grained, they only block concurrent access to the same row (or table in case of a table lock). With Oracle, a row lock does not even block queries to the same row (just other updates). So you should only encounter lock contention when the two applications are really updating the same shared table very frequently.
If the two applications do not share any data, then any locks on tables or rows will not affect the other application at all. They will only compete for global locks (very rare in sophisticated database servers) and shared resources (memory, server CPU, disk space, I/O and network bandwidth). If a single database server instance is not even close to being saturated when hosting the two applications, you do not have any problem here. When you see saturation, you can put the two applications' schemas on separate machines.