Hello.
The SMC JSV is only for the main applicant. That person is envisaged travelling alone to NZ, concentrating all their energy and resources on finding a skilled job. (INZ changed the rules from the old situation where the family could come along as well, since, if they started to get settled but no job was found, there was perceived harshness in their having to uproot themselves again, to leave when the JSV ran out.) When the main applicant gets a skilled job using the skill proved in the application, and gives INZ proof of this, the Residence visa originally applied for will come into action, and will give visas to any family members included in that, so THEN they can arrive in NZ.
Usually, it isn't possible to get a temporary visa for the partner, unless s/he qualifies for a visa in her/his own right. SMC JSV is specifically excluded from the list which entitles a partner-sponsored visa to be granted.
WF3.1 Who is eligible for a special work visa
Partners (see E4.1.20) of people granted work visas (including visas granted under Long Term Business Visas Category instructions) allowing a stay in New Zealand of more than six months may apply for and be granted a multiple entry work visa under these instructions,
unless their partner has been granted a work visa under any one of the following instructions:
Foreign crew of fishing vessels (see WJ); or
a Working Holiday Scheme (see WI2); or
Recognised Seasonal Employer (RSE) Work Instructions (see WH1); or
Supplementary Seasonal Employer (SSE) Instructions (see WH3); or
Silver Fern Job Search Instructions (see WL2); or
Skilled Migrant Category Job Search Instructions (see WR5);
domestic staff of diplomatic, consular, or official staff (see WI4).
http://www.immigration.govt.nz/opsmanual/
And we haven't heard lately of any visitor visas granted for partners in this situation - I guess the system shows up that they are the partner of a JSV person, and this throws doubt on their intention to leave NZ because of lack of reason to return to their home country.