Should fit, length might be slightly different. You could modify spring spacers to compensate. this is assuming you are talking about 4744 Ohlins springs and 25IDS KTech springs. I've used KTech stuff in Ohlins before. Measure first.
You might have to remove the spacer all together or just leave the base. Not sure if it's worth the hassle. I should just buy new.
They are interchangeable, as long as we're talking about the 4744-xx springs in the Ohlins NIX30 and FKR cartridge kits and the 36-260-xx springs in the K-Tech RDS and DDS kits. The ID, OD, and free length are a perfect match. Just remember that Ohlins measures rates in N/mm where K-Tech measures in Kg/mm.
I’ve got a couple of Ktech sets for sale. http://forums.13x.com/index.php?threads/k-tech-dds-rds-25ids-fork-springs-9-5.370320/#post-5827305