What is meant by Legal? What does a build need to be legal? Is it that it must actually work and it can get all its feats without cheating?
Yes, it must be able to be built as written. It's not really cheating that's the issue, although hacked characters are of course not allowed. Basically, the guild wants people to check their builds by actually creating them in a leveler program or some such module to make sure that what they are posting doesn't have errors that make them impossible to create as described.