Yes, the On Demand Router is the native load balancer for a WebSphere cell. Then you simply use the "weight" feature to control the distribution of requests.
Setting Weight - In the admin console, go to "Servers > Clusters > [your cluster type] > [your cluster name]" then under the "Additional Properties" heading click "Cluster members".
Set their "configured weight" to equal values and then ripplestart the cluster (or cycle individually). Note, "runtime weight" takes effect immediately but is reset to configured weight whenever the server is started.
Requests are allocated by a simple formula: (weight of Member X) / (Sum of all member weights)
so if server A has a weight of 20 and server B has a weight of 1, then server A should get 20 / (20+1) or 95.3% of all requests.
In your case, just set them to the same weight.