Do you have any evidence for this?
No evidence what so ever. Pure speculation. Here is the part from a previous post relating to it.
Doran also refers to his "friends at court". I believe this to be Varys. The Dornish have not had a prescense in the Capitol or the Court since the Sack of Kings Landing until Oberym came. Who else would have reason to be loyal to the Dornish over the new royal family? Varys is protecting Doran's nephew (Aegon, even if Doran doesnt know it) It stands to reason that there is a certain amount of trust and communication between the two. And even if theres not surely Varys would see through the strange marriage proposals made for Arianne, The Archons daughter being fostered by Doran and he would have knowledge of Dany and Viscerys where abouts when this happened.
It could be I am stretching my regard of Varys abilities as a spy master but we do not know how much he really knows about anything. GRR said himself, Varys will never be a POV cause he knows too much. Small parts throughout the whole series have led me to believe that Varys knows enough to assume that Prince Doran is plotting something if he doesnt explicitly know this. But if Varys is true in his Statement of serving the realm, and him and Illyrio are really trying to help a Targaryen reclaim their birthright then what I said could be true. To be sure there is no way to know until the series concludes(and maybe not even then) but its just a theory