There's no doubt that Mikogami let Tsukune join the Yokai High on purpose. He even made sure Tsukune had no other choice (after all, how can a mediocre boy possibly fail EVERY School Entrance Exam? Cause as far as I understand it, each School has its own Test and he does just fine with his actual grades in High School).
So the correct question would be, why ecactly Tsukune of all people?
I agree, that Mikogami wanted a human beeing as an ambassador, so people of both worlds could come to understand each other. And to fight for each other.
I'm sure, Mikogami had known for a long time about Fairy Tail and its goal to revive Alucard and destroy human kind. He has his eyes and ears everywhere
Hokuto was the first experimental Human-in-Yokai-High we know about. And I wouldn't say that the experiment was a complete failure.
Mikogami learnt this way for sure, that Yokai blood could change a human and that a 'Holy Lock' would give the user some control about it's transfomation.
The problem with Hokuto was, that he wasn't as naiv and kindhearted and openminded as Tsukune, when he entered Yokai High. He was fighting for his right to live for as long as he could remember. So it never occured to him to make some friends and fight alongside them.
And all in all, Mikagami created at least a kind of 'Doubleagent' (with Tsukunes help of course
). Otherwise, how would've Tsukune and the others ever learned about the Floating Garden let alone entered it, if not for the help of Hokuto and his boss?
So again, why Tsukune?
He seams nothing special and yet Mikogami went length to get him into Yokai High. Arranged for him to met Moka (I'm pretty sure it wasn't coincidental, that she was the first one he met. She never used that bike afterwards, did she? ) and with every step on his way, Mikogami knew what was happening with Tukune. Maybe he didn't plan it all in advance, but if he'd wanted to, he could have told Kuyou to stop... or maby not, cause it was all part of the plan, putting some preassure on Tsukune and his friends... you get my point
So, we wondered why Moka in her memories called him by his name, as he confessed to her, when she never should've heard of him at this point in the first place? Or at least should've forgotten by sealing her memories?
To make a long story short, we came up with the idea, that Tsukune may not be as pureblooded human, as everyone thinks he is.
Moka knew him obviously, he's adapting to the shinso power in an incredibly speed and he is the only one, who can remove the rosario. It was said, that he might have kind a similar aura like the 'actual key' or so.
Maybe because they were meant to meet? Maybe they're even fiancés? Pure blooded societies tend to get their children engaged early in many stories.
Some part of R+V reminds me of Katekyo Hitman Reborn. Or even Vampire Knight. An seemingly ordinary Kid learns that he/she is not the simple human they thought they are. The first inherited a special power through bloodline when the later is a sealed Vamp...
So, what if Tsukune is at least a halfblood? A childhood friend of Moka? Or even a relative?
I'd really loved to learn what would've happened, if Tsukune had drunken some of Mokas blood back in the first season...
That could've told us something about Tsukunes heritage, if not human. Wich is possibly why Ikeda didn't tell us...
At least, they are bloodbound, able to hear desperate callings for each other in times of need and capable to feel the others presence.
And only Ikeda knows how much of his human heritage (if there ever was on XD)still remains in his body. I'm not talking about his humanity/sanity, but how much his gens/cels have changed already. And if he's aldready suffering the same weaknesses. Since the first time Tsukune became a 'ghoul' we never saw him in contact with water again. But there has been a scene early in the 2nd season, where he holds onto the Rosario and is told, he's not that powerfull anymore (the Fight with the Doppelgänger). Just a coincidence? Maybe, maybe not...
In the matter of Alucard, I agree that won't be solved in the near future.
But Tsukunes likeness to him and his becoming a threat always shines through in times when Tsukune is desperate to save Moka and willing to do everything to save her. Didn't Akua say, Alucard went wild because he lost someone and kinda wanted the whole world to pay for this loss? Maybe it's the same with Tsukune. He always ends up 'freaked-out' when Moka is in need, never in Training.
btw, I like Tsukunes 'Berserk-Form'. Way better than Kaluahs 'Arm-transformed-to-Batwings'-one