The only issue I can see is the compstion of the solder itself.
Differing amounts of lead/tin ratios lead to differing mechanical strength, and brittleness, and also require differing temperatures to melt them.
A brittle water pipe jpoint is definately not desirable, and is we are talking fairly thin walled copper pipe, then higher temperature solder might also embrittle the pipe.
Since this pipe is at the back of a washing machine, one can imagine there will be a sloenoid shut off valve, and this will deliver a shock wave back into the pipework especially on closing and will find out any brittle joints.
I would chec your electrical solder alloy ratio and compare it to pulmbers solder, if they are the same than you will be fine.
BTW it is becoming much more common to use self sealing plastic connectors in outlet pipework these days, it is easier to install and mechanically extremely strong.