It's kind of unfortunate that the access is so restrictive to be honest. I can understand requiring the person to be flying Delta (you don't want your most premium credit card to encourage folks to fly with a competitor), but no guests (to match the Sky Club access) and a requirement to buy the ticket with the DL Reserve card is somewhat excessive. I actually wonder if Delta is paying Amex somehow for this benefit (by a debit against Amex's payments to DL for the Sky Club visits).
On the one Delta thread it sounds like the policy has been changed that the ticket has to be purchased with any American express, not necessarily the reserve card, but you do have to be a reserve card holder. Am Ex holders haven't able to guest people into the skyclub for a few years, the only way you can guest people in now at the skyclub is if you have an executive membership or chose the guesting benefit as a diamond choice gift or are flying international as skyteam elite or in J.
Seeing I'll be cancelling my platinum Am Ex on the renewal (due to the enhancements to the reserve), I'm going to have to remember to charge tickets to LAS on my Am Ex since my CSR card is my card I use for all travel expenses once the MQD spend waiver is met on my reserve.