Is hydrostatic testing prerequisite for tumbling a tank?

[WaterWolf]

I took my tanks in for their annual VIP and was told a couple of my steel tanks had some rust. The shop I took them to doesn't have a tumbler so they took them somewhere else to get the job done. The person they took them to said he could not tumble them without a new hydro. I bought these tanks new and they are not due for hydro until 2013. I've never heard of a tank requiring a hydro in order to be tumbled. Has anyone else ever heard of this?

Thanks,
WW