Yes, it is possible to attach your car as a cab in Ola as well as Uber. But this strategy is not that beneficial because to get incentive driver needes to complete 10 trips in a day. And it is not possible if you jump between Ola and Uber.
If you still want to attach your car with both then you can have two different drivers so that your runes for more time. In this case, there will be chances that you will get an incentive from at least one.
My suggestion is that you run your car for one cab service so that your payment and incentive process will be organized.