I think it was a win-win
I have known Nexsan since the beginning as a channel partner and from what little I know, I think the deal was a win-win. For investors, Nexsan probably didn't grow fast enough to make an interesting exit. After 12 years, I suspect the investors wanted an exit with a decent return - which they got. The problem Nexsan has is their hardware didn't fit a unique enough niche for tier-1 vendors to compete over (same goes for Exagrid now - they have no unique value prop and ultimately very few exit strategy options).
For Imation, they need to leverage their brand as the Nexsan brand alone probably isn't enough to take them to the next level.
One other note: Of all the storage vendors I've dealt with over the years, Nexsan had the best modular storage out there. It's a fast workhouse that never went down. Of all the vendors we worked with, we had the fewest support calls on Nexsan product - it's an incredible value for what it is. From a cost per TB perspective, Nexsan was always near the lowest cost and their annual maintenance costs are also some of the lowest in the industry. It's a well engineered, solid working modular storage solution.