Currently the only image formats still commonly used today that can be imported into custom controls are non-scalable bitmap formats. The only supported vector formats that I know of are WMF and EMF, which is almost never used anymore to my knowledge. Even worse, it doesn't support features now expected in vector formats, such as gradients and alpha transparency. So if you're developing a custom control, you have to either use an antiquated format or a bitmap format.
LabVIEW 2011 introduced the new Silver control set, which to my knowledge still use LabVIEW's internal PICC format, which is completely undocumented. Rather than adding gradients and other new features to this private, undocumented format and using that, it would have made a lot more sense to add support for SVG, a modern, full-featured vector format that is commonly used, and used that for the Silver controls.
Not only are the two vector formats LabVIEW supports ancient formats, but their inclusion almost seems like an afterthought. Imported WMF and EMF images aren't anti-aliased like the Silver controls. Because of this, it's practically impossible to create any modern-looking custom controls that look good scaled unless you don't want any diagonal lines or curves, in which case you might as well just use a bitmap.
Sorry for the abrupt end!
