Yep, there's many substitutes and they can be used for different reasons.
I prefer a lighter lubricant during colder months and a little heavier lubricant in the heat of summer. Dumonde Tech makes a freehub light oil and a grease. You can also use Dumonde Tech Liquid Grease. Shimano and Mavic also make freehub lubes. One of my favorites that is no longer available is Paul Morningstar's Electric Lube which is more of a very light grease.
However, these above are all freehub lubricants and you were seeking alternatives, perhaps beyond specific purpose freehub lubricants. You're in luck, because the DT Swiss uses the Star Ratchet that is very tolerant of thicker lubricants because of it's design, but keep reading as to why you might want a thinner lube. For winter I like using a lighter, thinner lubricant like the Dumonde Tech freehub Oil. You can use chain lubricant as well, but you might find yourself servicing the Star Ratchet on a greater frequency. But since it's so easy to remove and service, you can lube it with any good lubricant. I lube my on a pretty regular basis, so I tend to use lighter lubes. The freehub greases will keep them quieter a little longer, but create more rotating friction. Perhaps a better summer choice lubricant?
Additionally, the lighter lubricants will assist in reduced rotating friction. As you might have already noticed, the DT Swiss freehubs are not the best free-spinning rear wheels, so they can always use a little help. One thing that you will notice is how much quieter they will be. Some prefer the louder freehubs to the quieter ones. I prefer the stealth mode.
You might take a look at this link:
Reviewed | Dumonde Tech Freehub Grease and Oil | Competitive Cyclist