Active-Active means both Edge nodes are active for data forwarding and routing operations.  Each additional 'Active' Edge node also adds an extra next hop for the  T1/T0's to balance across, for example.

The above addresses 169.254.0.2/3  exist on each Edge node (T0SR) on an Active/Active Tier-0 gateway.  The forwarding table in the image is that of the Tier-0 DR on a host transport node.  If the Tier-0 were in Active-Standby, there would only be one next hop / default route.

ECMP (Equal cost multipathing) means multiple paths to a destination prefix can be installed in the routing table and forwarding table.  The load / packets can be balanced using a 5 tuple hashing algorithm with the available paths.

For example, the below is the routing and forwarding table with ECMP enabled and a default route advertised from both upstream peers.

ECMP disabled

The other thing to consider is, if you have a Tier-0 gateway configured with Active-Active and ECMP disabled, you could inadvertently discard traffic if uRPF is enabled, as traffic may be received on an interface the T0SR did not expect it on.

The behaviour of ECMP with the various protocols is the same, so I won't demonstrate between each protocol.

Let me know if this clears it up for you.

PS. I cover this topic in my book

Thanks