Last tested: Jan 31, 2018
Generally speaking, no. Each Looker user is only allowed one set of credentials for each type. So, you can't connect two email/password combos (or two LDAP logins, SAML logins, etc) to one Looker user.
There is a workaround of sorts that takes advantage of Looker's Alternate Login method. The email address associated with your LDAP account, for example, could differ from the email address you use for Alternate Login.