Technically 4* Tendo is a f2p Ninja.

You will get 80 of his frags for free though Ultimate Training (and when it updates). He is also 400 pulls in Tendo Treasure. So if you recruit him through a treasure first you already have a 3 star Tendo. Then when you're done with UT you'll need 20 more frags. Then there were events for weeks where you could get Tendo sometime after UT was released. Tendo was also in a box from Mission Mobilization multiple times, hell you can even get Tendo Pain in a chase mission. So it isn't too far-fetched to think that he is a f2p ninja.

(Yes I know that Tendo Treasure can give you Hashirama instead)

Hell even I had the choice of 4 star my Hashirama or get his skillbook Ninja God cause I got him 2x in Mission Mobilization. (I went with Ninja God skillbook) and currently I have 40 extra frags, mostly from his bond in your home.

But any ninja that was only obtainable through RNG (star level doesn't matter) is not a F2P Ninja. Masked Man is a f2p Ninja if you saved coupons and went for events that had him then kept saving. Same with Jonin Minato since they were not only in RNG Events. (Looking at Fate and Mission Mobilization for example)