They're more like states than anything else. Like How New Hampshire, Vermont, Maine, Masachusetts, Conneticut and Rhode Island form the New England region.
A region isn't a country. Kanto and Johto are bordering each other and are regions. Hoenn is an island state southwest of Johto. There was a map showing this that Latios made a long time ago and was based on a map in a Japanese magazine.
Either way, it's more likely that the regions are all states of the same country. The pokemon world's map is based on Japan. Hoenn is Honshu island turned 90 degrees for example.
Kanto is based on the real Kanto region in Japan. Also, there's a thing called the nationaldex which includes all the pokemon in the country. So, it stands to reason that Kanto, Johto, Sevii and Hoenn are part of the same country. As for Oore, it's its own entity. It's completely landlocked.
LX
Edit: Found a map. It was created by SPP's Latios and Pipikachu