Can a Tumblr user follow a wordpress blog?

Tumblr

Yes, there are embeddable follow buttons from Tumblr. Or you can use a plugin, it doesn't look like many of been updated recently. Jetpack has a sharing option that includes Tumblr and several other social networks.

But yes there are ways to import your Tumblr feed and/or send WordPress posts to your Tumblr.

Unless you are running on WordPress.com, then the answer is no. Not without some serious effort, basically easier to run your own install at that point.