Yes and no. You can use multiple buildpacks with an application, but those buildpacks must all be for the same stack. You cannot use a buildpack like Java which targets the cflinuxfs3 stack and a buildpack like HWC which targets the Windows related stacks. In that case, you would just need to push two different applications, which is generally the right approach.
>does yml supports multiple buildpacks for war and assembly?
Your application manifest.yml can include a `buildpacks` block which takes an array of buildpack names.
Ex:
buildpacks:
- php_buildpack
- java_buildpack