Hi Josh H,
You can setup your alert email with the token {{SP_Send_Alert_Info}} (Search the token list in the email editor). That token will populate your Alert Email with a link to the individual lead record. This link will allow your sales person to view the Marketo lead details, incuding activity log, without having to log in to Marketo.
Note that the link will expire according to the setting you have under Admin > Login Settings > Edit URL Expiration.
Let me know if this helps!