Q:

meaning of the phrase "though it may be"?

It is from Crash Course World History. It is at around 5 minute and 8 second. Here is the context:

Human beings, regrettable though it may be, are inherently vicious, and have to be restrained from their viciousness.

Would it mean the same if the host said it this way?

Human beings, though it is regrettable, are inherently vicious, and have to restrained from their vicikusness.

If he could, then why did he use may be?

A:

regrettable though it (may) be is a clause of concession with the subject complement fronted for emphasis.  
You can move such a clause around since it relates to the predication of the main clause, not to any one constituent:

The price, regrettable as it is, is over $10,000.
Regrettable as it is, the price is over $10,000.
The price is over $10,000, regrettable as it is.

Compare:

The price, sad to say, is over $10,000.
Sad to say, the price is over $10,000.
The price is over $10K, sad to say.

P.S. Clauses of concession historically were marked by the subjunctive (regrettable though it be) and may be could be a periphrastic substitute for subjunctive be,  use of which has been on the decline.  

