If you're using dmidecode, then you need the uuid set.  But, even with the hyphen format, usually dmidecode handles it -

uuid.location = "56 4d 1f bc b8 82 0a af-fe c4 2b a6 e7 04 0e a5"

dmidecode -t system

# dmidecode 2.11

SMBIOS 2.4 present.

Handle 0x0001, DMI type 1, 27 bytes

System Information

  Manufacturer: VMware, Inc.

  Product Name: VMware Virtual Platform

  Version: None

  Serial Number: VMware-56 4d 1f bc b8 82 0a af-fe c4 2b a6 e7 04 0e a5

  UUID: 564D1FBC-B882-0AAF-FEC4-2BA6E7040EA5

  Wake-up Type: Power Switch

  SKU Number: Not Specified

  Family: Not Specified

Notice the UUID matches the uuid.location.  Have you tried dmidecode -s system-uuid?  That number (with a little character manipulation) should get you results.