Yes you can. It isn't a matter of hiding it...its a matter of removing it from the "public" layout.
Make a second layout via the "Duplicate Layout" function. On the copy, remove the fields you'd like "hidden".
When you're in as admin, work on Layout#1. When showing it to other folks, use Layout #2.
Is this what you're after?
Thank you for your post.
Yes, you can limit the fields via Instant Web Publishing, just as you would in normal FileMaker Pro.
Pull down the File menu and select "Manage -> Accounts & Privileges". You will see Admin and Guest privileges as defaults. Click on "New..." and Create a TEST account. Make the password TEST. Under Privilege Set, select "New privilege set..."
Now, you have more detailed information. For each of the Data Access and Design, there are settings. Under records, choose "Custom privileges..." and we get even greater detail. This shows you all the tables. Select the table, and set View to "yes". Under Field Access, select "limited". Here you can set fields to no access, modifiable, or no access.
This should get you started. Please contact me if you run into any difficulty or want additional clarification.