By default, snaps run under strict confinement so are not able to launch other applications on the system. If they rely on some other application they should ship that themselves then they can execute it.
Otherwise there is a Process for reviewing classic confinement snaps where a snap can request to use classic confinement - in this case they are not confined at all and can launch other apps but this requires explicit approval and can only be done when is actually necessary for the snap to function and the snap fits within one of the established categories for classic confinement as outlined in that page.