Do you suppress the header row also? Or do you want to keep that? When I have done tables in code, I coded it like (vla-put-TitleSuppressed Tbl :vlax-false) and that worked for me.
I've tried
(vlax-put Tbl 'TitleSuppressed :vlax-true)
(vlax-put Tbl 'TitleSuppressed -1)
but never
(vla-put-TitleSuppressed Tbl :vlax-true)
I'll have to give that a whirl (though it shouldn't make a difference, should it?).