Writing this eight years to the day the question was posted, the landscape has changed, and China’s contributions to radio astronomy in particular are now quite significant. The question of accessibility, though, is a bit more complicated.
After the commissioning phase that began in 2016, the Five-hundred-meter Aperture Spherical Telescope (FAST) started full operations in 2020. With the loss of the Arecibo Observatory later that year, FAST quickly became even more important than expected. For a number of astronomical objects, it is the only telescope capable of detecting them. Its capabilities are impressive; an example I like to cite to illustrate this is the Galactic Plane Pulsar Snapshot (GPPS) survey, which has discovered over 500 pulsars in about four years. To put this in perspective, that’s about 10% of all pulsars ever discovered – and GPPS is only one survey.
Nor is this the end – or even the apex – of radio astronomy "mega-facilities" in China. At least two fully-steerable radio telescopes are at some stage of design or construction: the Qitai radio telescope (~110 meters in diameter) and the Jingdong radio telescope (~120 meters), either of which would be the largest single-dish fully-steerable radio telescope in the world. My understanding is that you can picture them as slightly bigger versions of the 100-meter dishes at Green Bank and Effelsberg. Qitai was originally supposed to begin operations this year, but construction apparently only began in the fall of 2022. 2022 also saw the completion of the Daocheng Solar Radio Telescope, and there are plans to build up to five more telescopes like FAST.
In short, China is rapidly building some of the most important radio astronomy facilities in the world.
The question of accessibility and openness to the international community is less straightforward. An example of this is simply who has been allowed to submit proposals for time on FAST. The first call for proposals, in 2020, was limited to only Chinese astronomers. The second call, in 2021, allocated about 10% of observing time to international astronomers. I don’t know what the proportion will be going forward – proposals for this year are still under review – but the plan is to make time increasingly available to international astronomers. This would be in accordance with astronomy’s generally accepted "open skies" policy, which allows folks from anywhere to propose for time on an observatory. (10% would certainly be comparatively low, but hopefully we do see a significant rise.) With information about Jingdong and Qitai hard to come by, it’s not clear what the future holds.
Most data become available to all after a 12-month proprietary period, to protect the teams that originally took it. This is a common practice worldwide and a fairly reasonable time span. The exceptions to the policy are data from the commissioning and testing phase, as well as data from Director's Discretionary Time proposals and other "reserved data", none of which will be made public.
The short answer, then, to whether e.g. American astronomers can use FAST is a definitive yes; if you want examples, it’s quite easy to find papers with American authors using FAST data on the Astrophysics Data System. I certainly hope the same will be true for the steerable telescopes; it would take pressure off of facilities that I'd assume have received even more proposals after the loss of Arecibo, like the GBT and the Giant Metrewave Radio Telescope.
Some of the difficulties with openness can be attributed to tensions between China and other countries, both scientific and political. Collaboration absolutely happens, but it’s not easy. Even things like getting the actual data from FAST once you've taken it can be difficult; the ideal method of data transfer is to copy it to hard drives and ship them, a pain under any circumstances but obviously even more so in the present climate.
I’m less familiar with the Chang’e missions, but Peter Erwin noted that Chang’e 3 results have been published, and some international scientists are indeed supposed to have access to samples from Chang’e 5.
