Yes, the individual can sign in to Skype for Business as a guest to join a Skype for Business chat as long as they have a meeting invitation.
In your meeting invitation, click Join Skype for Business Meeting.
Type your name in the text box to sign in as a guest
Make sure to select the option to install the Skype for Business Web App plug-in.
Click Join the meeting.
In the dialog box that displays a choice to run or save the plug-in file, click Run, and follow the prompts to install the plug-in.
Depending on the meeting options set by the meeting organizer, you’ll either enter the meeting right away or wait in the meeting lobby until admitted.