Yes it bloody well is cheap!!
You're not playing the game here, rather you are trying to hide your units through outside means. It would be fair enough if your opponent didn't pay attention to where you'd put your unit; hell, it happened to me a while ago, and when I realised what had happened, that they'd been deploying whilst I'd been messing about and so a Dev unit had been put in the perfect place to ambush me, I was annoyed as hell with myself. And if that was as far as you were going, that would be cool. But now, you want to deliberatley obscure you opponent's view by outside means.
If you both like to play hidden set-up, or do this kind of thing anyway, then go for your life. But if this isn't a routine thing, then it is without doubt a cheap trick. Hell, if you had to ask then it suggests that you already know this.