Is there a better way of detecting if a Spring DB transaction is active than using TransactionSynchronizationManager.isActualTransactionActive()?
No better way than the TransactionSynchronizationManager.isActualTransactionActive(). It is the utility method used by spring to handle the transactions. Although it is not advisable to use it within your code, for some specific cases you should - that's why it's public.
Another way might be to use the entity manager / session / connection and check there if there's an existing transaction, but I'd prefer the synchronization manager.