I think we can safely safe that some "operators" choose to use Glocks but I doubt Delta Force has some uniform issue of firearms and while the official pistol of the Seals is the Sig I'm sure some are given permission to use Glocks as well. The description above of the unknown operators having a number of different pistols is probably accurate of what is actully happening at the top of the food chain. For some, the Glock will be the best choice, while others will step up to Sig, HK, 1911, etc. These customized for rough usage 1911s and CZs make sense:
http://www.customwinslow.com/#/home