OK, a worthy argument. First, I agree, none of the OM type rifles were actually assembled by the Army, I did not mean to imply they actually built them. But, my opinion is they had them assembled for the SS from Army stocks to supply the SS with scoped rifles to fill the TO&E requirement, and I believe by the mount maker myself. I agree with most everything else.
However - you ask "how many guns do camp guards need" - very few I imagine. So, read the 1940 order - the SS Training and Replacement Battalions were excluded from receiving arms from the Wehrmacht stocks, only units actually engaged in field operations under the Army were allowed access. So - who - the entirety of the SS Replacement Divisions. Remember, later in the war the SS was raising a lot of new divisions, which means even more recruits (foreign mostly) and training battalions for those divisions. The supply of reworked Gew98 rifles was already in the SS Ausbildungs und Ersatz Battalions. any expansion would require more rifles. IMO the depot at Dachau was set up to suppply the training battalions specifically, especially since the army order forbid the use of Heer rifles for those battalions. I never researched the size of training battalions vs field battalions, but I suspect they were large and would probably be easy to get troop numbers for.
Now - do I think NONE of the SS contract guns ended up fielded by WaffenSS units at the front? No, but it was very concerning to the Army that they might get mixed in with HWa accepted arms (which was the purpose of the rune marking originally).
For instance - I had one verbal report of an single rune 98k captured by a 101st div vet. Supposedly, it was taken from as SS guard post on the way to the Eagles Nest. This is a perfect example of a unit with no access to Army weapons that still needs a rifle. Sure, its anecdotal, but my point here is there are a lot of men in the SS divisions that did not see front line service but still needed weapons. I saw one question why you find single runes in used condition - training unit use would cause wear more/equal to combat use. Also, a lot of SS contract guns you see are new condition, even 43 dated ones, indicating possibly depot captured. All fanciful stories for sure, but you have to expand the idea of what SS units used 98k's and realize the depth of the SS organization, which you do.