Can an employer refuse psychological information from an employee?

Yes and no, in that the law does not make them accept it, read it, and keep it, any more than the law makes people accept, read, keep, etc. any relevant or important documention--you can throw out invoices and wait to see if you're sued, throw away contracts so you don't know what your rights are, refuse to read summons & complaints served on you and wait for the consequences, etc.
But no in that they cannot avoid the consequences of being presented with information, especially if you can document that you sent it to them (e.g. use email to confirm that you sent them the infomation and generally what it is, but they returned it; e.g. an email to HR saying "This is to confirm that you have returned to me the documenation I provided regarding my [insert condition here] . . .") If you put them on notice that you have a disability, then if you need a "reasonable accommodation" at work, they cannot claim ignorance of your condition, simply because they choose to not read or retain it.
Bear in mind, however, that even if you have a condition that qualifies as a "disability" under the law (due to its effect on your life or functioning), and even if your employer is aware of it, you can be terminated legally for *behavior* or *actions* at work, even if they grow out of the condition. Example: you cannot be terminated for being bipolar. But if during a manic phase, you get unfocused and fail to complete a project, or act inappropriately at work and disrupt the workplace, you can be terminated for that. The protection for disabilities or medical protection is only protection against being terminated for having them (and the requirement for *reasonable* accommodations)--it does not protect you if fail to do your job, make errors at work, or act inappropriately at work.