If an Employee is dismissed during his 3-months probationary period is he or she entitled to receive any accrued holiday pay?

Yes, the Employer must calculate the holiday entitlement from the commencement of employment until the final date of termination.  This relates to the statutory number of holidays.  If the contractual number of holidays is in excess of the statutory minimum the Employee should also be paid subject to any specific clause in the contract of employment.