If you use the Pipeline snippet generator to generate a 

tool

step, it will let you choose Git as the tool type, and then will let you choose from your configured Git tools to get an output like this:

tool name: 'git-2.0', type: 'git'

Jenkins will then cheerfully ignore this and use the default git tool on the system, not throwing an error or anything. The documentation of the tool step indicates that only maven, gradle, and jdk are supported, but the syntax generator doesn't limit the user at all.