I agree. A letter of intent is not the same as a contract but check the wording carefully.
If they say to you to enter the UAE on a visit visa rather than provide you with an employment entry visa, then you should be fine. If they get an employment entry visa issued, that means they have started the process to issue residence visa and work permit, and there could be problems if you change your mind.
Some more information here...
http://www.dubaifaqs.com/teaching-in-dubai.phphttp://www.dubaifaqs.com/visa-ban-uae.php