Are cancerous lymph nodes typically identifiable on a chest x-ray?

Not always. A typical chest xray is not very sensitive in finding abnormal lymph nodes. The best radiographic tests are chest cat scan and pet/cat scan when indicated.
Sometimes. Enlarged mediastinal nodes can be seen on chest radiograph. These usually are related to tumor or infection. Tumor can be primary lymphoma or metastases from other primary tumors. Infection can be related to TB, coccidiodomycosis and histoplasmosis. Some other less common bacterial infections can also be cause.
No. Chest radiograph lacks good sensitivity for the identification of lymph nodes. A ct of the chest is a better staging method for cancer and to identify enlarged lymph nodes.