Haven’t heard of any, but thats not to say there arent any, some builders just quietly do there own thing. The rotec is definately a viable option. This is whats so good about experimental aviation. Just heard about another first flight at Narrogin. Rotary powered glider tug. No idea of the setup though.
For me I’m happy with Tracy’s EC2, seems pretty good for the application. Although there are a lot of wires to go through tracking my personal RFI gremlin.