Having worked for both traditional security dealers and IT/Security Integration companies, I have been stuck on both sides of the fence.
The security dealers I worked for were comically afraid of any interaction with IT staff/departments, and would always either defer to customer staff for network design input, or subcontract to a partner company. I could appreciate that they knew the limits of their average technician and engineer; but they did have 4-5 Cisco Certified staff members on board, and were one of the largest Cisco VMS/Access Control dealers in the world (which isnt saying much...).
The IT/Security Integration companies I have worked for were obviously living in the IT infrastructure world daily, as larger HP/Enterasys/Cisco/Meru/Fluidmesh partners (having a full range of certified wired and wireless certified technicians, and RCDDs in some cases). On the flip side, there can be times that the networking sales team can over think and over complicate their piece of a deal and just muddy up the entire opportunity; so each has its own set of headaches.
Every networking manufacturer we have worked with typically have 1 or 2 good regional support reps/engineers if there is design or BOM work that needs a ton of resources thrown at. Most/all good sized manufacturers in that world have factory field rep support, not rep firms like the security industry will tend to have. A lot of IT distribution houses (Ingram/Synex/Jenne, etc) are just order takers and don't provide too much design support from what I've seen