Hi Harikrishna,
do note that what you guys have done is actually not officially supported by SAP.
You should not connect the Database supporting an SAP application instance directly through the DB layer to another application, no matter whether it is another DB, in the risk of losing the relational integrity of the SAP data model in the SAP application owned tables.
Of course, if all you do is read external tables through DB Link, that risk is virtually zero, but still, SAP reserves the right to question the architecture you have created. Specially if there are stored procedures within the Oracle DB where the SAP ERP instance is installed to use those DB Links.
That being said, as Fernando pointed out, you have two possible alternatives in a HANA environment. The probable less disruptive one is SDA, which you can even understand as "HANA's DB Link on steroids" (since it goes beyond the simple DB federation use case up to query optimization, etc.). Basically, you create a virtual table (aka proxy table) in HANA pointing to the external table/view in the remote Oracle DB instance, and then you can consume that virtual table normally from HANA or from the NW ABAP application layer on top of that HANA DB.
The other option would be leveraging the secondary DB connection from the NW ABAP Layer itself (which is the same principle that SLT uses), but would involve additional configurations that you don't have today. Also, the connection to the remote DB would now be done via the ABAP layer and not through the DB layer, so you need to take that into consideration and the impact that would bring to your developments.
I'd probably go with SDA for your case.
Best regards,
Henrique.
PS: by switching to HANA as your DB, the restriction to use DB native features in the DB instance which is underneath an SAP Application do not exist anymore, and you would be fine using SDA with your ERP HANA instance, and even create Stored Procedures or HANA views with them if you wanted to. BTW, with NW 7.4, you can consume views & procs directly from the ABAP layer.