I did hear a rumor that there is Jumbo Kesar in the Dominican Republic. That rumor came out of South Florida. Could this be remotely possible and is there any way to verify this?
Pretty much all I know about the Dominican Republic is that they have bad liquor.
Could be another false rumor 
Not only is it growing in the DR, it's growing on a very large scale commercially. the scions were brought directly from India, and they were put on mostly Banilejo rootstock.
This is the first video I recorded with Noris Ledesma, they had three varieties in the initial phase of the project, Kesar, jumbo Kesar, and Kent, they later abandoned the Kent, this video is mostly in Spanish.
https://youtu.be/JCnW56M77YwI did a follow up on the project, a year later, this video is in English
https://youtu.be/D2-bJ_0bh1Elast information I got on this DR project , Joe, left the project and started one of his own ( With Kesar), the original project, was expanded, if memory serves me, around 30,000 trees. they were shipping containers of fruit to NY and Chicago markets, but had some serious logistics problems, at that time, the project did not have their own packing processing plant, and the area does not have a thermal treatment plant. on top of that, since Jumbo Kesar are much larger than the local varieties normally exported, the thermal treatment plant really screwed up a few shipments, some of the mangoes were cooked. also you may have noticed, how the fruits were in many stages of development, in commercial setups, fruits must be extremely close to the same stage of ripeness, and that was another reason they had some failures. I do not know if they worked those problems out by now.
I was told by a person that they planted Jumbo Kesar in South Fla, but want to keep that persons name private.