Yes, because reptiles make vitamin D in their skin when expossed to UVB, and they can regulate how much or how little they need to make. The D3 powder supplement should be just that, a tool to fill in any gaps but not to be depended on entirely. Too much dietary D3 can be terrible, where as you could be fine without it as long as you have access to UVB.
IMHO your chameleon should get UVB light to produce its D3. As long as it can move in and out of the UVB it can regulate the D3 and won't get an overdose from it. D3 from supplements, however, can build up in the system and lead to an overdose and health issues so you need to be careful with it. There's no real data on how much is too much when it comes from supplements which is why we recommend only using a supplement with D3 in it a couple of times a month and leaving it to produce the rest of it from the UVB exposure. It's important to dust with a phos - free calcium powder at most feedings though.