No, unless it is obvious collusion or someone is clearly getting taken advantage of then there should never be a veto. Ever.
If someone wants to make a bad trade because they dont think it is a bad trade then that is their problem.
My Main League
10 Team Standard Score League:
QB: Roethlisberger, Freeman
RB: R Rice, L McCoy, R Mathews, A Bradshaw, D Sproles, B Brown
WR: R White, V Jackson, W Welker, S Smith
TE: J Graham,
K: S Gostkowski
DEF: Seattle (this week)