Nah.
Here's how my last games have gone:
As the Ottomans, I had an alliance with Austria and Russia.
As Germany, I allied with France late in the game. France. You know, the same country that I took Alsace and Lorraine from. (France was diplomatically isolated after a Great War and I was the only one to offer them a hand in open friendship!)
As Japan, I pursued and eventually got an Anglo-Russo-Japanese Alliance to block a militant USA.
As Persia, I managed to maintain a cordial "Asian" Alliance consisting of Russia, the UK, and eventually China. (The UK dropped out soon thereafter.)
As Austria, I allied with Prussia and Russia... After dismembering Prussia in two wars so I could form SGF.
I used to think the AI simply would never ally if you owned its cores, but as my examples demonstrate, GPs are willing to overlook the ownership of cores IF they are alone and unloved in the world.