Think you should do fine. Vehicles are good against daemons- make sure you make as little space for his units to deep strike in- play for mishaps! Daemons suffer from dakka in my experiance and gun boats should do fine. Biggest concern is the flamers, they are painful for everything- again just spread and play for mishaps.
Changes, well perhaps load the venoms with splinter cannons trueborn and put haywires on the wyches to deal with soul grinders. I play against daemons quite regularly and find that splinter cannons are great, and reavers, if you have any also do great but in large squads. Think you have to emphasize your mobiity, don't be affraid to fly right away from his units and shoot them as they try to catch up.
Delicious and Coven-Baked for your Pleasure
A very slow, 30K Salamander Distraction Log: VULKAN LIVES