Reverse Filling A SCBA Tank (That is What The Paintball Shop Called It?)

Just a question? I have a SCBA tank with a standard 300 DIN valve that I need to get filled and have always had it filled at one dive shop in my area that can fill to 300 BAR or 4500psi. That shop is now gone and no other dive shop in my area can fill to 4500PSI. I called a paintball shop and thy said they can fill it just fine but what he said didn't seem to make much sense to me as I have never heard of filling a SCBA tank in this manner. He said that they will just use my fill whip that has a female foster fitting and connect his compressor using a male foster to my fill whip and fill my tank in that manner and NOT fill through the valve itself (This is the only way my tank has been filled is through the valve itself) So my question is will this even work and is it even safe to fill a tank in this manner as I have never seen it been done before or should I just run away?