The passage in Mark is consistant with the statements by Jesus about ?good tree/good fruit, bad tree/bad fruit? in Matt 12:33-35 and Luke 6:43-45, and somewhat with what Paul wrote in I Cor. 12:3 (??no one who is speaking by the Spirit of God says, ?Jesus be cursed??). The teaching appears to be about consistency?that goodness and light cannot coexist with evil and darkness. I think this passage is saying that if someone has joined you in doing God?s work, that?s a good thing. Not only does it benefit the work of the kingdom, but if someone is joined in the efforts, they are not going to work to hinder that at the same time. It wouldn?t make sense for them to knowingly work in harmony with God and against him at the same time.
The value of this work to the one(s) supporting the work of God would depend on motives and how they live their personal lives:
?Many will say to me on that day, ?Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?? Then I will tell them plainly, ?I never knew you. Away from me, you evildoers.? (Matt. 7:22-23, NIV).
So it looks like it is possible to openly work for God?s kingdom, yet live an unrighteous personal, hidden life. Now this we know very well to be true. Kingdom work without personal value can also be done for selfish motives, such as greed or to gain attention to oneself (see Matt. 6:1-8, 16-18; Acts 8: 9-24).
Back to the original question of whether or not this teaches religious tolerance?you can say it does within a limited context. These people were properly using the name of Jesus to liberate the oppressed as Jesus did and the same way the disciples had been doing even though this group had not been officially authorized with the 12 (Matt. 10:1). This is fine for as far as it goes. The same actions were done in the name of Jesus as the disciples did, so this glorifies the name of Jesus and accomplishes the work of God. There is no mention what, if anything, these outsiders were teaching along with these works. There didn?t seem to be any deviant doctrines as of yet. The only issue seemed to be, ?Is Jesus sent and approved by God?? Miracles done in his name answered, ?Yes!?
Once Jesus left the earth, different teachings sprang up. The writers of the NT letters definitely had limits as to what differences were acceptable (e.g., the letter to the Galatians, and 2 John 10-11 chastises anyone in the church who gives aid and comfort to false teachers).