Well, I think there's risk there, and yes, I think that is an indictment against Gardenhire. I don't think it means he's incompetent - it just means he has some weaknesses, and this seems to play on one of them. He also has his strengths, and overall, I think the strengths dwarf the weaknesses.
But this seems to play on a weakness, and I'd be happier if Kubel wasn't an option. I'm worried about Arcia and Parmelee's playing time. (And I recognize I might be the only one worried about Parmelee's playing time.)
Arcia is going to be in the lineup every day most likely, and if he isn't it means he is struggling quite a bit and needs more time in AAA.
The leash with Kubel would be short I imagine, let's just say he comes on like gangbusters in ST and earns a starting spot (likely DH). If he struggles the first 3-4 weeks of the season I can't see the Twins waiting to cut him loose.
I'm not really worried about Parmelee's playing time at all. Parmelee has shown next to nothing his last two seasons on the Twins, either he is going to flat out earn regular playing time or he isn't.
Other than Parmelee the only guy he really takes potential at bats from to start the season is Doumit, and maybe Plouffe later on (once Sano is up). I don't see a real issue there, since if Kubel is getting at bats on the reg, he is probably preforming. However, he absolutely should be in a platoon at the absolute most.