Hello Narad
In this topology, yes both the ABRs will generate the default route, and the stub router will have an equal cost to all networks in Area 0. Thus, both routes will be placed in the routing table, and thus traffic will be load-balanced across both ABRs.
Now how that load balancing will take place depends on various factors. One way to load balance is indeed equal-cost multi-path (ECMP) routing. This allows the packets from a single flow to traverse multiple paths. This can cause problems in packet reordering and MTU differences in the various paths, and this can disrupt the operation of some protocols, especially TCP, or VoIP applications.
For this reason, Cisco has employed CEF, which, regardless of the routing protocol being used, is a routing mechanism that aids in the methods by which such traffic is transmitted. Take a look at this post for more information about load balancing and CEF:
Actually, equal cost routing, with the appropriate precautions, is actually beneficial and desired in production networks.
I hope this has been helpful!
Laz