If you're doing any edits that are not supported by your RAW editor, you'll need to save in a format like TIFF or JPEG. There's a very limited amount you can do in most RAW editors.
Limited maybe, but unique to raw editing. The OP asked if he should save as tiff or some other lossless common format instead
of proprietary DNG. That would be unwise as there are edits you can do to DNG files (in a raw editor) that you can't do with non-raw formats.
I would even question the need to convert the original raw files to DNG at all, that is, until it becomes necessary to do so (ie when you no longer have a raw editor which can open your camera raw files). As long as you have a copy of Adobe's DNG Converter you can convert them then.
Carry on processing your camera's native raw files while ever it's possible to do so, convert them to tiff for further editing in a non-raw editor. If you do insist on converting them to DNG as a future-proofing measure, don't delete the original camera raw files! They are the the only "true" originals you have.