Never tried it unfortunately, had to move on. I'm hard pressed to imagine how spring could cause the inability to find a class from a completely different maven library. If the issue does have something to do with spring, personally I'd call it a defect with the ES maven library, as an external dependency shouldn't cause class resolution problems.
Similar post (no maven though): Could Not Initialize Class PreBuiltTransportClient
Personally my opinion is that we should just let the TransportClient get deprecated, ignore this issue as a very uncommon situation, and for anyone reading this post, they should move on to using the RestClient or RestHighLevelClient.
Thanks for your continued help and support!