Definitely NOT systemd. Android’s init is pretty primitive.
I’m not sure if there is an order in which they are executed, BUT, I can tell you that init is parallel, so even if they do start generally in some order, you can’t count on the first one being in a ready state before the second one needs it.
You pretty much have to use the service disabled, on property a=b enable and start approach to guarantee that it does what you need it to do.
HOWEVER, there is probably another way to do what you’re trying to do.
For example, combine the two services into a single binary, and do a fork/exec within it, or, since one of your two services depends on the other, why not perform a startup synchronization within the dependent? As a really simple example, while (otherserviceisnotavailable()) sleep(1);