"as I understand it 3 disk RAID 5 CANNOT run w/ two failed drives"
You are correct - a RAID 5 can lose one disk and stay up and running; a RAID 5 cannot lose two disks (RAID 6 can).
"they spoke w/ Dell determining that 0 and 1 had failed; which is odd b/c they were able to get the system running"
Only slightly more than half of disks that go offline do so because they are actually bad, so with the unlikelihood that two disks would have actually failed at the same time, it is not odd at all that they were able to get it up and running again - in most cases, after some careful investigation as to which disk should be chosen, one of the offline disks would be forced online, and it will begin functioning again.
"outsourced tech team I use took three hours to determine that the system was offline ... I figure if its unresponsive, that determination happens rather quickly"
Yes, agreed, however, if they had access to a DRAC card, they may have been investigating log files to determine exactly what happened before shutting down and what the possible cause was. Three hours seems excessive though, even with all that said. Even if they were investigating log files, etc., it should have been VERY clear, pretty quickly, to a trained server tech what the situation was (this can depend on the system in question too - low-end systems often are not equipped with needed diagnostic tools/displays.
"I'm trying to figure out if they incorrectly assessed the situation"
They ultimately made a correct assessment - and they made a good decision to call Dell if they were unfamiliar with what to do, rather than try to wing it. While it might be helpful to have someone familiar with technical terminology on the phone with Dell, anyone could have called and been walked through the procedure of troubleshooting and repairing, and if I were to give you any advice, it would be to look around to see if there is another local tech team you could work with that is more familiar with Dell hardware and RAID in general.