Is it legal to use IntellIJ Ultimate Edition Student License to work on commercial product
According to this entry in JetBrains' Licensing and Purchasing FAQ:
Students and teachers are eligible to use JetBrains All Products Pack (including IntelliJ IDEA Ultimate, ReSharper Ultimate and other IDEs & tools) free of charge for educational purposes. Educational licenses cannot be used for commercial purposes.
from JetBrains TOS(emphasis mine):
- GRANT OF RIGHTS
3.1. Unless the Toolbox Subscription has expired or this Agreement is terminated in accordance with Section 10, and subject to the terms and conditions specified herein, JetBrains grants You a non-exclusive and non-transferable right to use each Product covered by the Toolbox Subscription for non-commercial, educational purposes only (including conducting academic research or providing educational services)
so you're not allowed to use it on a commercial product.