No it would be considered tampering.
They wouldn't be rostered with another club so how would it be considered tampering? I assume you would need a USA Hockey number for insurance purposes, but what's illegal with letting a kid come practice? This is exactly how my son started. He was playing roller hockey and wanted to try ice. I reached out to our local club and they said he could come out and practice with them, but since it was after the 12/31 deadline, he couldn't be on the actual roster and play games.