Yes, of course they have. They are devices aimed at the same market and im sure many people only buy one and have a decision to make/made.
No doubt, despite what some posters here are wrongly telling you, that Sony has lost customers to the 3DS. Games like Resident evil revelations, Tales of the abyss, SSF43D, Kingdom Hearts 3D prove that there is a hardcore market in the 3DS. Its not as big as it is on the home consoles but its definitly there and its sizeable enough to be atractive given the lower development costs.
Despite that, yes Nintendo games obviously still sell the most. I personally have a 3DS and have only bought Zelda OOT3D from nintendo cause of the special edition 3DS that came bundled with it.
With games like Fire emblem, Monster Hunter 3 Ultimate, Bravely default, SMT4, Monster Hunter 4, Dragon Quest VII... a hardcore would be crazy not to go for the 3DS instead of the Vita.
