Can Hadoop be beneficial when data is in database tables and not in a file system
'SQL' on Hadoop is very much a thing, though I use quotes since it's probably more accurate to say it's SQL-like. Some options for bringing SQL-like capabilities to Hadoop include Hue, Hive/bee (Heading towards Stinger? So punny Apache), Impala, SparkSQL (probably not a great solution for a bank given the possibility of concurrency issues), among others (Seems like everyone has their own version of it these days)

To be honest though, if you're asking if it could be helpful, you probably don't need Hadoop (sorry in advance of that comes off harshly, it's not intended to). Lots an lots of places think they need Hadoop, but very few actually need Hadoop. There are of business that are down on the tech because they transitioned to it when the need didn't really exist. If you truly do need Hadoop or another distributed system it'd be almost impossible to determine which setup would be beneficial to your org without an intimate understanding of your data, and your specific business means.