Are numpy's basic operations vectorized, i.e. do they use SIMD operations?

Yes, they are.

/*
 * This file is for the definitions of simd vectorized operations.
 *
 * Currently contains sse2 functions that are built on amd64, x32 or
 * non-generic builds (CFLAGS=-march=...)
 * In future it may contain other instruction sets like AVX or NEON     detected
 * at runtime in which case it needs to be included indirectly via a file
 * compiled with special options (or use gcc target attributes) so the binary
 * stays portable.
 */

Link: Numpy simd.inc.src on github.