Unfortunately, this is not an easy question to answer. It really depends on what state you live in and the types of crimes for which you have a conviction. In some cases, the amount of time since the last crime makes a difference also. In most states, anyone who has a criminal past may have to go before the nursing board before receiving a license. Those boards have a considerable amount of leeway when it comes to granting or not granting a license.
In most states, no one found guilty, pled guilty or pled nolo contendere to a felony could get a license in any medical profession. On the misdemeanor side of things, there are certain types of crimes that will exclude a person from being in the medical profession, as a nurse or any other role. These include cases involving elder abuse, child abuse, sexual assault, or violent assault of any kind. The medical boards in all 50 states have an obligation to protect patients from medical professionals that could be a threat to safety and well being.
All states require every applicant for an LPN license to undergo a background and criminal check. For those who have a clean record, the board checks that provision off and goes on to the next. When they see you have a misdemeanor in your past, it raises flags that you will need to answer. In most states, part of the application process asks whether you have a criminal record. Answering truthfully is the first step. If you do not put it on your application, you stand less of a chance of getting your license. They will likely ask for a written explanation also. Again, truthfulness will go a long way. If this conviction was many years in the past, most states will give you clearance after a hearing.
If you obtain your license as an LPN, you still have some hurdles to overcome. All employers will look into your background. It is a legal obligation. If they see the conviction, they will have questions. In addition, some will outright refuse to employ you. They are liable for any threat an employee poses to a patient. However, like the licensing boards, time and type of crime does matter to some employers. If you did a minor crime 20 years ago and have a clean record since, it makes a big difference when compared to a conviction a year ago with pending charges.