Is Veigar a viable champion for ranked?

yes hes completely fine for ranked

https://lolalytics.com/ranked/worldwide/platinum/plus/tierlist/

Statistics say yes.

He's not bad for stomping low Elo. If you can stack well and shut down your enemy laner than it should be fairly easy to climb with him.

Bronze to gold yes. Maybe plat.

You can build tank items on him and do fine off his infinite scaling. I played him as support and did well last time. Built like ninja tabi and dead man's plate to help me zoom in for cages. Of course disregard this since I only played him once this season.

The best stun in the game ? yes.

In high elo there are times that he is a pain in the ass. The zoning can be annoying at times when this little devil's team is ahead and all... But doesn't happen too often. His laning phase doesn't feel too safe and extremely squishy, If he low enough, someone will dive.