While the owning of the bird may create dust that may not have been there, if one is allergic to environmental items, it would be wise to eliminate any source.
Allergic reactions are very specific to the person suffering from the allergy. The most important thing to know is if the person in question is allergic to feathers. If so, then there may be a conflict. The best thing to do is get allergy testing and go from there.
I have never heard of an African grey plant. I am not sure how many people on average are allergic but people can be allergic to anything and everything. If you are talking about the bird, yes people are allergic to their dander as well
Yes, you could be allergic to your African Grey. Allergy's differ between people. Try using a HEPA filter, medication or getting rid of the African Grey.