We absolutely can (and should!) be using keys instead of login/password for the PowerConnect.  The CLI command:
crypto key pubkey-chain ssh
should enter a configuration mode for setting SSH public keys on the switch.  Page 35 in the CLI manual at ftp://ftp.dell.com/Manuals/Common/powerconnect-5524_Reference%20Guide_en-us.pdf
For SNMP, the PowerConnect supports SNMP v3 security models, which include public/private keypair authentication.  See page 178 of that same guide, and see http://www.snmp.com/products/techinfo/secmodels.shtml