Could a 4 pole 3.5mm jack be used to power a RGB LED?
Technically, yes, it would work.  But it's probably not a good idea.  Here's how this family of connectors tends to perform, including TRRS, TRS, and TS of any size:


They're typically used with analog line-level signals that can reach up to +-15V in some cases, so voltage is not a problem for you.
They're not suitable for high currents because of the small contact area.  If you're running 1A or less in total, it's probably okay, but I'd want to verify specs if my estimate got above 100mA.  I say "in total" because the common return has the same rating as any other contact.
They're not suitable for hot plugging or unplugging without careful analysis because they rake the contacts across each other.  If you imagine a plug or unplug event in slow motion, think about the different circuits that are made each time a jack's contact crosses a boundary between the plug's contacts.