The answer is no, you can't print the labels with another printer different than a Postek one. Typically, developers create the applications that work only with the physical devices they posses. Of course, there are free products that you can use with any compatible printer you want, but those are expensive and sometimes lack support for the labels you need. You actually need a Postek printer in order to print the needed labels.
I recommend contacting the developers in order to obtain an official response: Elaine.firstname.lastname@example.org