Migrate a 3 Tier App with Oracle DB from on-prem Physical server to AWS EC2

Hello.

The following AWS document introduces the flow of migrating on-premises OracleDB to AWS using DMS.
https://docs.aws.amazon.com/prescriptive-guidance/latest/patterns/migrate-an-on-premises-oracle-database-to-oracle-on-amazon-ec2.html

For database migration, determine how much downtime the system can tolerate. If sufficient downtime is available, we recommend the simplest possible migration method that allows batch migration.
For Oracle migration, use a migration method such as Oracle Data Pump.
If there is not enough downtime to tolerate, we recommend a migration method that allows incremental migration.
Migration methods include Oracle GoldenGate for Oracle migration and AWS Database Migration Service (AWS DMS) for other migration methods.
Although the differential migration method can minimize downtime, it is more challenging than the batch migration method, so please plan prior research, verification, and rehearsal.

looking for confirmation as whether Oracle DB server can be migrated using MGN itself or need to use DMS as its a DB

Using Database Migration Service means the end state will be Oracle running as an RDS database instance. You cannot use DMS to migrate a database onto EC2.

See the Homogenous tab of https://aws.amazon.com/dms/ , there's no getting away from it.