RAC has serious limitations when it comes to transactions and locking. For instance all work does as part of a single XA transaction has to be done on the same RAC node. RAC is really a joke in a lot of ways - first clue is that they have to give the product a name that tries to convince you it is "real application clustering" when it has such strong limitations.
These limitations lead to people having to be rather creative in how they configure datasources in clustered WLS (for all applications, not just Quartz) because it is rather likely that two connections obtained from a datasource during a tx will NOT be to the same RAC node.
That all said, there are a number of folks using Quartz 1.6.x and 1.8.x with Oracle RAC - there is not a fundamental problem with Quartz in this respect, just a matter of configuring Quartz with datasources that a sure to make proper/consistent use of RAC nodes.
This old mail thread regarding RAC and Quartz may be of interest:
also this doc has interesting info:
also googling for weblogic and oracle rac find all sorts of stuff.