Even more complex objects requiring multiple colors get drawn in
Illustrator to the exact pixel size, and then pasted into Photoshop as a
Smart Object. It is a last resort, though — gradients aren’t dithered, and
editing later is more difficult.
If you need to use a bitmap for a texture, there are three options: use a
pattern layer, a pattern layer style, or build a bitmap layer at the 2× size and
turn it into a Smart Object. I prefer to use pattern layer styles in most cases,
but be warned: patterns are scaled using bicubic interpolation when you
scale the entire document, so they become “softer.” The solution is to create
two versions of each pattern, then to manually change pattern layer styles
to the correct pattern after scaling — a little tedious, but totally do-able
approach.