Let us discuss King Viserys I

[Rhaenys_Targaryen]

Rhaenys,

by that time, the Velaryons have long been close allies and kin of House Targaryen. But I doubt that anyone had any interest to make the Arryns or any other great house a dragonriding family. The fact that Laena claimed Vhagar during a time in which the Iron Throne was not necessarily on good terms with the Velaryons (it does not seem as if Laena had already claimed Vhagar in 101) suggests that she may have inherited Vhagar from another Velaryon/Targaryen family member (Aerea or Rhalla, if one of them married into a cadet branch of House Velaryon).

Speaking about that. It seems that incest was totally a Targaryen thing. Else, I think, Corlys and Rhaenys would have married Laena and Laenor to each other to continue their line and show the Realm that their line was as pure and royal as Baelon's...

By 92AC, the relations of House Velaryon and House Targaryen were already detoriating.. And at that moment, Laena had not yet been born.

As to the incest thing.. If Rhaenys and Corlys had wanted to make a stand, against having been passed over in 92AC, marrying Laena and Laenor to one another would have been the thing to do, no? Even after 101AC it could have been done.. Laena had been betrothed from the age of 12.. That would be 105AC.

[Lord Varys]

I guess the Velaryons may have gained/earned the right to ride dragons at an earlier point, thus it would have been already common in 92 AC. Jaehaerys and Viserys could then not really take away there dragons. And the Velaryon precedent really would have been a good example as to why other houses should not be granted dragons.

The fact that Laenor was not married to Laena suggests that the Velaryons did not dare go through with such a provocation, possibly because only the Iron Throne could give permission for an incestuous marriage. Else that would really have been the smart thing to do.