Different Creative Commons licenses impose different requirements. After thinking this through more carefully I think you will be able to use CC-BY-SA licensed music in your podcast provided that you present it as a properly attributed independent work. This may or may not fit within your artistic vision for your podcast. It seems that collective works are a red herring, as e.g. CC-BY-SA 4.0 doesn't mention collective works at all.
In 3(a) and 3(b), the license makes a distinction between reproducing the work (also inclusion in a collection), and creating and reproduction adaptions of the work.
In 1(a), and adaption is defined as basically any change or derivation other than inclusion in a collection.
In 1(b) a collection is defined (emphasis and bullet points mine):
"Collection" means
- a collection of literary or artistic works, such as encyclopedias and anthologies, or performances, phonograms or broadcasts, or other works or subject matter other than works listed in Section 1(f) below,
- which, by reason of the selection and arrangement of their contents, constitute intellectual creations,
- in which the Work is included in its entirety in unmodified form along with one or more other contributions, each constituting separate and independent works in themselves,
- which together are assembled into a collective whole.
- A work that constitutes a Collection will not be considered an Adaptation (as defined below) for the purposes of this License.
Errata: 1(f) seems to be a typo and should point to 1(h). The Adaption is actually defined above.
Your use of a 30 second version of a CC-BY-SA 3.0 licensed music as an intro in a podcast does not qualify as inclusion in a collection as defined in the license, because it is not included in its entirety in unmodified form.
Therefore, your podcast would be an adaption of the CC-BY-SA 3.0 licensed music. Under 4(b), this effectively requires you to license your podcast under CC-BY-SA version 3.0 or later.
The CC-BY-SA 3.0 does not deprive you of rights you would have anyway (see the next sections).
The license makes no special provisions for collective works because these terms are unnecessary: Your applicable copyright laws already govern collective works. The inclusion of the CC-BY-SA 4.0 licensed work within a collective work would be a reproduction of that work, as allowed by 2(a)(1)(A).
About collective works.
Creating a collective work does not give you extra rights to other people's work. However, there's a huge legal difference between a collective work that contains other author's works which has an independent copyright, and a joint work where multiple authors collaborate and therefore share the copyright. In the CC licenses, this is phrased as reproduction vs. adaption.
Collective works also assume some amount of editorial control over selection and arrangement of the contribution works; this is mostly relevant for copyrightability of the entire collective work and is irrelevant for licensing of contribution works.
Within the CC licenses, mere reproduction puts fewer obligations on you. I.e. the CC-BY-SA licenses only require attribution in case of reproduction.
Speculation
For a reproduction, the reproduced work should be perceived as an independent work that is merely included here.
This is e.g. given for a blog post that includes a CC-BY-SA licensed image, as the image is visually and physically independent from the text and is usually attributed directly below the image.
In an audio work such as a podcast, I would expect an independent work to be attributed / announced before or after it is played. The attribution can be “reasonable”. However, I don't think external attribution in the podcast description would be sufficient. Attribution within the podcast itself may be required. This isn't necessarily obtrusive if you already have a section for thanks and acknowledgments. For example I could imagine closing with this:
You: Thank's again to Guesty McGuestface for talking with us about advances in p-hacking! Next Wednesday, we'll discuss 7 things we learned by overfitting a machine learning model.
The theme music is “Test Sounds” by Jane Doe, used under *inhales* creativecommonsattributionsharealikethreepointzero.
Have a great week!
McGuestface: bye!
[theme music starts playing]
Without clear demarcation within the podcast, your podcast would have the character of a work that is adapted from the music. It would then be necessary to license the podcast under CC-BY-SA (see the above discussion for the CC-BY-SA 3.0).
