I would agree that public proponents of Intelligent Design and YEC creationism are intentionally excluded from mainstream scientific publications, scientific institutions, and scientific jobs. That appears to be essentially accurate. I am not sure who would dispute this.
The real question is why they are excluded and if this reason is unfair.
In specific the case of the Grand Canyon access, it is possible that the exclusion was not justified or fair. At the same time, there is a perceived history of misrepresentation of science by these groups, so some might argue that excluding those with this track record is justified. I am sympathetic to both sides, because I think individual scientists should be assessed separately for their honesty and compliance with the ground rules of science in their scientific work.
We already know that he is not doing science under the rules of the rest of us. He has signed the AIG belief statement, in which he promises to ignore any evidence that points to an old earth. That is not "science" as we understand it. Even AIG agrees that they do science in a different way than the rest of us.
I'm not exaggerating the AIG belief statement's requirement:
By definition, no apparent, perceived or claimed evidence in any field, including history and chronology, can be valid if it contradicts the scriptural record
This means he has promised to declare "invalid" any apparent or perceived evidence that supports an old earth. There is also great examples of this happening among AIG scientists. If I was in charge of this process, I would ask him to specify how he would report evidence for an old earth that he discovers. If he could not give an honest answer, I would reject the application because it is by definition not a scientific inquiry into the age of the earth if only one answer is acceptable. This would not be based on prejudice, but the public belief statement of his organization.
I agree that good science can, in principle, be published outside peer review. I also agree that because it is clear they are excluded now on principle, it is not fair to level this as an unqualified critique. Once again, it is important to ask if is fair exclude them.
The bigger problem is that their arguments are not good science, and the mathematical arguments often have large errors. I have not had good experiences in my attempts to directly approach ID proponents with informal "peer-review" of their work. I cannot think of a single case where an error has been retracted or fixed. That is concerning, and does not foster trust.
Related, there is a journal that accepts ID submissions (BIO-Complexity). Ignoring the scientific quality in these articles (which sometimes have important content), look at the number per year. It is pitifully low. About two articles per year, many of which are not actually original research. For comparative reference, I am submitting two peer review articles this week alone to journals from a small scientific group with just 3 graduate students. ID appears to have hit a major dead end in terms of coming up with new ideas.