Yes it is. Tumblr's parent is Yahoo and Yahoo will be keen on being friendly to the developer community to attract top talent. Much of which reads HN.
I was just at dinner with an ex-Zynga game dev last night who had never even heard of it.
Well, he did say "top talent"!
This friend of mine was laid off in New York and received his severance; based on what I know about him, he could work in a multitude of places right now if he wanted to.
Zynga's vilified image aside, there is no reason to believe their engineers are not "top talent."