Scylla is a drop-in replacement for Cassandra, so yes, the configuration is exactly the same.
Key configuration details:
1. storage.backend: your choice of cql, cassandra, or cassandrathrift. Since Thrift is deprecated, you'll probably want to go with cql. If you choose to go with Thrift, make sure you enable Thrift on your Cassandra/Scylla nodes.
2. storage.hostname: comma separated list of Cassandra/Scylla nodes, localhost is the default.
3. storage.port: defaults to 9042 for CQL, or 9160 for Thrift, so you can leave this out if your nodes use the default.
4a. storage.cql.keyspace: name of the keyspace to use when using storage.backend=cql
4b. storage.cassandra.keyspace: name of the keyspace to use when using storage.backend=cassandra or cassandrathrift.
I'll assume you are using the pre-packaged server distribution, in which case the conf/gremlin-server/gremlin-server.yaml uses the property file conf/gremlin-server/janusgraph-cassandra-es-server.properties. Best to stop the server before making any property file changes.