There's a Linux system command that reports hardware specs at /usr/sbin/dmidecode
This command has massive output about every single thing in your system, down to each individual memory module, you want to look for the section "System Information".
The piped command grep -A8 tells the shell to look for the line "System Information" plus 8 lines below.
# /usr/sbin/dmidecode | grep -A8 'System Information'
Manufacturer: Red Hat
Product Name: KVM
Version: Not Specified
Serial Number: Not Specified
Wake-up Type: Power Switch
SKU Number: Not Specified
Family: Red Hat Enterprise Linux
The line you're looking for is "Manufacturer".
In my case above, it's a KVM virtual server running out of a Redhat Host.
In case of VMware virtual servers, Manufacturer will show as "VMware, Inc."
In case of physical server, the Manufacturer line will show known hardware vendors such as IBM, Dell, HP, Sun, etc...