In this scenario, the IP addresses in your network will appear in IPAM as if not in use, or Available.
This will change when we implement Indirect Discovery. With Indirect Discovery we will be able to pull accurate IP status even when ICMP is blocked. I have a post that lists what we're working on What We're Working on for Orion IPAM.
Can you give some examples of when you need indirect discovery? What are examples of when icmp is blocked?