One of the interesting aspects of the START I and INF treaties is the participation of non-nuclear weapon states in the treaty inspection and notification activities. Official accounts of START and INF concentrate on Russia and the United States, but other countries participated in the verification activities as well. Here is an official statement from Jamie Mannina, the spokesman in the Department of State's Bureau of Arms Control, Verification and Compliance, who kindly clarified the issue for me:
Twenty-five years after the signing of the INF Treaty, it remains a landmark achievement in nuclear arms control. As a result of the INF Treaty, the United States and former Soviet states have eliminated an entire class of U.S. and Russian missiles -- all ground-launched missiles with ranges between 500 and 5,500 kilometers. The Treaty entered into force on June 1, 1988 and, by the end of its elimination period three years later, 2,692 U.S. and Soviet missiles had been destroyed. With respect to your questions:
Following the dissolution of the Soviet Union, the United States recognized twelve former Soviet states as Parties to the INF Treaty through succession. Of those twelve successor states, six had inspectable INF facilities on their territory (Belarus, Kazakhstan, Russia, Turkmenistan, Ukraine, and Uzbekistan). Turkmenistan and Uzbekistan each had only one INF site on its territory and those sites were inspected by the United States and then eliminated under the terms of the Treaty. Subsequently, Turkmenistan and Uzbekistan did not participate in the Special Verification Commission or on-site inspections. Inspections at U.S. sites were divided up among Belarus, Kazakhstan, Russia, and Ukraine as agreed by the inspecting Parties.
The United States, Belarus, Kazakhstan, Russia, and Ukraine continue to exchange required INF Treaty notifications. Those notifications are not releasable.
Under START, Belarus, Kazakhstan, Russia, and Ukraine had inspection rights in the United States. Each Party did, in fact, participate in some START inspections in the United States. That participation was as agreed among those four Parties. The bulk of START inspections in the United States were conducted by Russian START inspectors. The United States did conduct START inspections in Belarus, Kazakhstan, Russia, and Ukraine.
When the INF Treaty was signed in 1987, it was viewed as a remarkable success for U.S. foreign policy and for the NATO alliance as a whole, a success made possible by allied unity and perseverance. It remains an inspiration for future work.
It's a bit puzzling why the INF data exchange documents are not releasable, especially given that the INF treaty was published in full (with base coordinates, photos, and all) in the U.N. Treaty Series (Vol 1657, No 28521), but it's good to know that they exist.