Sir, Lightroom isn't even the best workflow for raw files. It's DEFINITELY not the best workflow for scanned files. Use Bridge.
But yes, I would suggest noise removal, as well as other adjustments such as Exposure and White Balance, in ACR before proceeding to Photoshop. The effectiveness of the noise removal will depend on the uniformity of the noise, I figure. Some extra care, eg with Dust & Scratches filter, will likely be needed in PS as well.