Is it okay having two vocal teachers?

It is not ideal to have two voice teachers, because you may be given conflicting vocal advice.  

A person does not need 2 of them.

Among those of us who are fine teachers of voice or any instrument - we would be INSULTED if a student had a second private teacher.  It is not unusual to have a teacher in school - and then, another private teacher;  the school environment only allows a limit amount of time for instruction,. and also - a fine private teacher who is a specialist in your are, can probably give you better instruction.  This is NOT a hard and fast rule - many of us taught school, and also had a second life as respected performers, etc.  But there are teacher in schools - in ANY subject - who got the education needed to be certified and land a school job - but actually are not at all any kind of advanced specialist. Sad - but true. And many school teachers will encourage good students to find a teacher that can work with them more in depth, and bring more insight.  but this a above board, and common - if you are HIDING from each teacher that you have another - not good . .