[Randomization in an initial block]

It is possible to set RNG seed for each process in a module (always_.., initial, etc.). To do this it is necessary to have a process handler:

module dut();

   int i;
   process P1;

   initial begin
      P1 = process::self();
      #2;
      i = $urandom_range(0, 500);
      $display("The value of i is %1d", i);
   end

endmodule // dut

Now you can set seed for each process individually:

module top_tb;

   initial begin
      #1;  // Wait process handlers to be created

      // Set seeds
      dut_a.P1.srandom($urandom);
      dut_b.P1.srandom($urandom);
      dut_c.P1.srandom($urandom);
   end

   dut dut_a();
   dut dut_b();
   dut dut_c();

endmodule