Sales intelligence is the data that tells you who to target: company firmographics, contact details, technographics, and buying signals. It is built for assembling lists and prioritizing accounts, but it stops at who to contact, not how to actually reach them.
Sales intelligence tells you who to target; relationship intelligence tells you who can get you in. One builds a list, the other gets you a meeting. They answer different questions, and the second is what turns a target into a conversation. See the full comparison.
The two are complementary: use sales intelligence to choose the accounts worth pursuing, then use relationship intelligence to find a warm path into each one. A good list with no route in is just a colder version of the same problem.
Via is the relationship-intelligence layer that sits on top of your sales intelligence. Once you know which accounts to chase, Via shows you who in your network can introduce you, so the list becomes a set of routes in.