No, the WB is just a tipster, similar to how law enforcement agencies have anonymous tip lines, and they are anonymous for a reason, to encourage tips.
It's not that they believe all the tips, they don't, but they are just starting points. If a tip is confirmed, it's the law that accuses ( the DA ) NOT the tipster.
See, the tipster is not the victim, and since the accused has a right to face the accuser, given that the tipster is not the accuser, the accused has no right to face the tipster. The tipster is the information provider, the accuser/victim in this instance is the United States, and so the accuser is it's representative in law, the District Attorney ( or State's Attorney in some states ).
If someone is going around lighting fires in forests, and someone leaves a tip that leads to the arsonist's arrest, the arsonist has no right to face the tipster, the tipster is not the victim, the United States is the victim, and the one accusing the arsonist of a crime is the united states via the DA.
Capiche?
The WB policy is more elaborate, but the principle is the same.
Given that the salient points in the WB memo have been confirmed by aids in the state department, bringing the WB into the hearings is, redundant, unnecessary, and Could lead to crazies harming him, and that kind of intimidation is what the President wants, in order to discourage more whistleblowing in the future.
No can do, sorry.