Hello Pradyumna
Yes, it is possible to use a static default route on the spokes and use a routing protocol on the hub. You still have to configure the routing protocol on the spokes as well, however.
The advantage of using the summary route is that all routing is dynamic and nothing has to be configured statically. This means that if you change your IP addressing of the hub or if you add new spokes, you don’t need to modify or configure anything beyond a simple routing protocol adjacency, and all the appropriate information is exchanged.
I hope this has been helpful!
Laz