这三个词组用法是类似的：
to some degree也作to a degree,与to some extent是一个意思,意为‘partly'
to a/some degree的例句:
To some degree I think that's right,but there are other factors which affect the situation
to some extent的例句：
To some extent,she was responsible for the accident.
以上参考：The Cambridge Advanced Learner's Dictionary
在The Cambridge Advanced Learner's Dictionary中未收录'in a way'这一词组.在GOOGLE中显示in a way在使用上确实不如这两个词组普遍.
In a way意为To a certain extent,with reservations; in some respects.
例句：
In a way I like the new styles.
You're right,in a way; but we have to consider the price.
可以看出,如果用'in a way'的话,这上面两个例句中,是可以用另外两个词组代替的.使用上没有区别.