What kind of cracks? Longitudinal? I am not familiar with epoxy repairs, but how about sistering a steel channels to the sides of the beam? Are there any signs of distress - other than the cracking?
It can be done if need be. You need justification from empirical data from somewhere (manufacturer, university/government study, etc.) that quantifies the bond strength to the wood. Manufacturers of structural adhesives (>400 psi bond strength) will tabulate allowable bond stresses for APPROVED materials and applications. However, you haven't given much information to help out. We need the following items:
1. A photo or diagram to indicate what you are talking about - a photo is better, along with a description of the 'cracks' i.e. lengths, orientations, and depths through the section.
2. Support conditions and span
3. Type of loading and location of beam in structure
As cliff234 mentioned, it is important to know the type and extent of distress. As an example: Quite often, checks in wood are not a controlling factor as they may appear to be very deeply gouged, but are in fact not important.
Have you attempted to determine the species and grade the piece of wood, per the applicable grading agency? If the 'distress' is within the tolerances of the grading that you require, there is no need to perform a fancy and unnecessary repair.
