From OpenAI's terms:
(c) Restrictions. You may not (i) use the Services in a way that infringes, misappropriates or violates any person’s rights; (ii) reverse assemble, reverse compile, decompile, translate or otherwise attempt to discover the source code or underlying components of models, algorithms, and systems of the Services (except to the extent such restrictions are contrary to applicable law); (iii) use output from the Services to develop models that compete with OpenAI;
(j) Equitable Remedies. You acknowledge that if you violate or breach these Terms, it may cause irreparable harm to OpenAI and its affiliates, and OpenAI shall have the right to seek injunctive relief against you in addition to any other legal remedies.
Those two very clearly establish that if you use the output of their service to develop your own models, then you are in breach of the terms and they can seek injunctive relief against you (stop you from working until the case is resolved).