Hate's not an issue, get a thief you pricks
However against the majority of mobs you'll xp off in your tanking career, war/mnk won't be pretty. Basiclly what everyone else, too much damage, sucking too much mp. Although war/mnk is the best tank in the game until 30 and maybe 37, no questions asked, so it's quite easy to be fooled into thinking they do better later in the game.
However there is absolutely nothing wrong with war/nin against many mobs. I've had a few war/nin tanks 50-60 and they have been quite good. Not sure about hate without thief but with thief( since I'm thief and was obviously there ) it's not an issue at all.
Chain 5 means it works, and I've gotten chain 5 with war/nin tanks so that's enough evidence for me. They're negating 6-12 hits so that helps balance the little more damage they take per hit. And they're dealing good damage while tanking so the mage's end up with the same mp really after every fight as they would with a pld tank.
The battles go noticablely faster so that keeps mp for the mages over time as long as the true DDs aren't gimp and are making the battle go fast like they should. Having a war/nin tank, a thief, and a solid dependable DoT like drg,rng, or mnk is like having 2.5 - 3 DDs without losing a tank. If a mage is running out of mp it's really their fault OR the DDs fault because they're not killing it fast enough. This tank is going to absolutely shine in a good party, or it's going to crash and burn more than any other tank would when working with retards.
In closing, you're going to suffer after 40 definitely as a war/mnk tank. I'm not going to stop you from attempting it but you probably won't enjoy its effectiveness as higher levels. pld/war and nin/war are popular wanted tanks, you'll get invites as them if you don't suck. And I hope my paragraphs showed the potienal war/nin as quality tanks on exterme ends of the spectrum. Like I said, they'll shine over the others in many ways assuming everyone else is good they'll take the party higher than the other tanks could. But in bad parties they'll only make it worse. And lastly be prepared to tank or damage as a war, this is a very costly job if you want to be great at it, which means the best gear for DD and tank which means millions and millions.
Edit: After reading that alla guide to war/mnk it looks possible at times, with galka or elvaan. You see galka's are better than everyone else so <Tough> <Luck> for everyone else.