It is completely allowed, following certain guidelines:
I am also taking this opportunity to point out that transfering credits with royalty system or market is not allowed, exept for services done by the other commander.
And
Credit transfers clarification:
Donations are excluded, your are not giving your credits, but rather donate on behalf of another.
Services would be designing, giving coordinates, helping to attack someone or clear a system, etc.
Helping a friend or alliance member in need is allowed, as long as you help him out, not power-level him on a regular basis.
What is not allowed is giving away credits on a regular basis for no apparent reson than to get the other commander to the same or close rank position, or make his power 10X what he had, in order to become stronger or modify the top 20, power-leveling a commander by giving him credits it did not work for in any way, leaving the others that played the game and got there hard at a disadvantage.
God Speed!