creating a tar archive from maven deploy

I am trying to use maven v3 to create a tar.gz output for a non-Java project in order to deploy to nexus. I cannot specify tar in the packaging option in my pom file. Unless mistaken, I can specify tar as an option for packaging when running mvn deploy. Is there anyway I can specify that in the pom file itself?

You can create the TAR.GZ file and "attach" it to the primary artifact. I have an example to repackage a WAR into Linux service on GitHub. The key steps are to package the assembly:

<project ...>
    ...
  <build>
    <pluginManagement>
      <plugins>
        ...
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-assembly-plugin</artifactId>
          <executions>
            <execution>
              <phase>package</phase>
              <goals>
                <goal>single</goal>
              </goals>
            </execution>
          </executions>
          <configuration>
            <attach>true</attach>
            <formats>
              <format>tar.gz</format>
            </formats>
            <descriptorSourceDirectory>src/main/assemblies</descriptorSourceDirectory>
          </configuration>
        </plugin>
        ...
      </plugins>
    </pluginManagement>
    <plugins>
      ...
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
      </plugin>
      ...
    </plugins>
  </build>
</project>

<attach>true</attach> installs the artifact. The assembly in this case is:

<?xml version="1.0" encoding="UTF-8"?>
<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.0.0
                      http://maven.apache.org/xsd/assembly-2.0.0.xsd">
  <id>bin</id>
  <baseDirectory>${artifactId}-${version}</baseDirectory>
  <files>
    <file>
      <outputDirectory>bin</outputDirectory>
      <source>
        ${project.build.directory}/${project.build.finalName}.jar
      </source>
      <filtered>false</filtered>
      <destName>${artifactId}.jar</destName>
    </file>
  </files>
  <fileSets>
    <fileSet>
      <outputDirectory>bin</outputDirectory>
      <directory>${project.basedir}/src/bin</directory>
      <includes>
        <include>${artifactId}.conf</include>
      </includes>
      <filtered>true</filtered>
    </fileSet>
  </fileSets>
  <dependencySets>
    <dependencySet>
      <outputDirectory>lib</outputDirectory>
      <useProjectArtifact>false</useProjectArtifact>
      <includes>
        <include>*:*-x86_64:*</include>
      </includes>
      <scope>runtime</scope>
      <outputFileNameMapping>
        lib${artifact.artifactId}.${artifact.type}
      </outputFileNameMapping>
    </dependencySet>
  </dependencySets>
</assembly>

but you'll need to find/create one appropriate for your use-case.