Vance was great buddies with Poul Anderson and Herbert, but everything I have heard him say about Herbert was always in terms of a tongue in cheek amusing scoundrel kinda thing.
Vance might be the only sci-fi author of any note that stopped reading his peer’ work, at least according to him. He has stated he had never read Dune, despite living with the Herberts in Mexico when Herbert had the kernels of the book. Robert Siverburg was buddies with Vance for decades but has stated Vance had never read any of Silverburg’s work. Looking at how unique Vance’s work is, I find it plausible.
Freegards
To me sounds like he meant it but maybe he didn't intend for it to come out it did. You could definitely tell though he still had a great fondness for Poul Anderson.
Interesting how he avoided reading his peers. Maybe concerned he would lose his uniqueness if he did? By the way, don't know if you're be care to read this or not but here's a nice write-up that first introduced me to Jack Vance (the site also introduced me to RA Lafferty): http://greatsfandf.com/AUTHORS/JackVance.php
So far i've only read one thing of his, the first Dying Sun book, but i'm planning to read the Lyonesse series soon.