Can multiple versions of the same dependency be used in a single Maven repository?

No. Maven will only resolve one dependency in your module and will omit the other versions to avoid any conflict. Even if multiple versions of the same dependency are used in the whole dependency hierarchy, Maven will pick one version using the “nearest in the dependency tree” strategy.

It is possible to specify different dependency versions using different profiles. For each version of Bukkit a profile can be defined and activated. Still if you activate more than one profile, only one version would be used.

<profiles>
    <profile>
        <id>Bukkit_1_7_9_R02</id>
        <activation>
            ...
        </activation>
        <dependencies>
            <dependency>
                <groupId>org.bukkit</groupId>
                <artifactId>craftbukkit</artifactId>
                <version>1.7.9-R0.2</version>
                <scope>compile</scope>
            </dependency>
        </dependencies>
    </profile>
    <profile>
        <id>Bukkit_1_7_2_R03</id>
        <activation>
            ...
        </activation>
        <dependencies>
            <dependency>
                <groupId>org.bukkit</groupId>
                <artifactId>craftbukkit</artifactId>
                <version>1.7.2-R0.3</version>
                <scope>compile</scope>
            </dependency>
        </dependencies>
    </profile>
    ...
</profiles>