Yes, a cluster of blisters on the penis could potentially be caused by conditions other than herpes. Other possible causes include:
1. Genital warts (caused by HPV)
2. Syphilis (a bacterial infection)
3. Molluscum contagiosum
4. Allergic reactions or skin irritation

It is important to consult with a healthcare provider for proper diagnosis and appropriate treatment based on your specific symptoms and medical history.