No, I don't think it will hurt your slalom skills at first. I think that using the Go when training for the first time a new move or manoeuver is a wise choice if you do not want to damage or break your iSonic. The Go is more forgiving and thoughter than the iSonic, so it's a very smart idea in fact.
However, you will have to repeat the same move on the iSonic once you will master that on the Go. This is going to be more difficult (lighter & wider hull, harder rails, faster scoop-rocker line, etc...), but do not despair, this is how you will make progress and how your slalom skills will improve.
Once you will be competitive and highly skilled, you will want sooner or later to change the Go for another iSonic, but smaller this time to get more response and to go faster. This is a normal process in the future, no worries. Take your time and enjoy the Go for now while improving your skills step by step.