No.
A sour mash is some portion (as low as 10% or as high as 100%) of the grain mashed and left overnight or longer (up to 3 days) to sour. It is then boiled and made into beer. Sour mashes are very unpredictable in my experience, mainly because it is difficult to maintain an elevated temp for a larger mash over long time periods. When a sour mash goes bad, it goes very bad.
Sour malt is, as a previous poster noted, sprayed with food grade lactic acid at about 2% by weight. Beers soured with sour malt are one-dimensional in my experience. Note that with a Kentucky Common, you're probably just looking for "tart" and not sour.
The sour beers of Belgium are *usually* fermented normally, then soured in barrels. Lambics are an exception here as in just about every area- they are exposed to the local microflora and go through a complex biological process.
Now. When I tried a Kentucky Common, I went whole hog. 8 pound grain bill, 100% sour mash for 3 days. I just wrapped the cooler in a blanket and went on vacation- it dropped from 150 to 105 over 3 days. It was very tart, but not what I would call "sour". I would estimate it was about as sour as 1500ppm lactic acid would give.
Now with 2% sour malt at 10% of the same 8lb grain bill, I get an estimated (8lb/bill)*(.10 1/bill)*(16oz/lb)*(28.3gm/oz)*(.02 lactic)/(20 liters/batch)*(1000ppm) = 360ppm lactic.
Translation: I would not expect this beer to be particularly sour. For comparison, a truly sour gueze is up around 4000ppm, while a berliner wiess might be somewhat less.
It all depends on what you're looking for, though. I believe ODaniel does 2% sour malt in some of his, which would be just enough for a subtle bite. If you're not a huge sour fan but want a little bit, another option would be to start low and dose with 88% lactic at bottling to get it higher if you want.
In terms of taste quality, I would rate a well-executed sour mash = lacto d. > sour malt > 88% lactic.
Hopefully some of this is helpful to you.