Without giving away any major plot points, I got Maven to erase Vald's debt, but every time I approach him (patrolling the estate grounds) he just attacks me. He's very easy to kill, but I wanted to take the high road in this instance. Has anyone successfully delivered the note to him without bloodshed?

No.

In fact, I was trying NOT to kill him myself but as I strolled by the gated backyard he teleported (glitch/bug) outside and swung at me. He IS aggressive, you're right.

Talk to him through the gate. He attacks you only after you pick that gate lock.

Im afraid not - he turns hostile when you try to talk to him

however i got it working

open console - target him, type

setav Agression 0

you can now talk to him

Tried this, but doesn't work for me.

Perhaps it might work, if you type the correct spelling of "Aggression"?

Just cut his throat =P

That's what I did anyway.

Confirmed. As soon as you open that gate, Vald goes perma-aggro. He'll talk to you before that, no problem. I went back and tried it again without ever picking the lock and getting the Quill etc. worked fine.