Can knitr::spin() pick up global options?

Yes, there is a way: as when knit'ing, just set global options in an initial setup chunk.

So, for example, the following spins up just fine, resulting in output that does not echo any of the supplied code.

#+ setup, include=FALSE
opts_chunk$set(echo=FALSE)

#+ aChunk
plot(rnorm(99))

#+ anotherChunk
1:100