Yes but Dell's ability to execute is limited by their relatively low end product shoe horning Ocarina into a backup appliance, IBM's is that they lost focus and fell hopelessly behind with the Dilligent product. Exagrid is post process and although it scales out, each node isn't particularly large and scale out is still limited to relatively small environments.
HDS Just bought Sepaton who despite being one of the first to market and being very scalable have had a number of directional changes and struggled for mind share as a result. With HDS in the driving seat they could get much more focus going forward but given their relative complexity I doubt they'll be able to take huge market share.
EMC with Data Domain have a good product and are way ahead of everyone else in terms of market share, ecosystem support and thus their ability to execute. Technically they look to be falling behind the likes of HP, but the backup market, especially SW and appliances has always been sticky, once you have footprint you're in for the long haul.
HP has the more scalable and arguably more functional solution these days. However they've traditionally struggled with the wider backup ecosystem support. That looks to be changing though as the StoreOnce product gets more focus and matures.
There are also plenty of software only solutions out there, but these don't tend to stack up at scale where some of the bigger appliances play and if you have a big appliance at the core, it typically makes sense to have the smaller appliances at the edge.