I know it sounds like the setup for some dumb joke, but I think it highly probable that it did happen. Consider, they were both Oakland residents, well known writers and they both liked to drink a lot. From 1903 when The Call of the Wild was published to 1913 when Miller died they were the two most prominent authors Oakland had to offer. They also had sojourns in the Klondike in common.
In 1899 when London sold his first story Miller was so famous that in San Francisco gossip about him made the front pages. From then until Miller's death in 1913 the two of them were the most prominent literary personalities in Oakland. It seems very likely that their paths must have crossed. I have no idea what that interaction would have been like. I have not found any statements by either one about the other. Collegial drinking buddies? Possible, as I have noted they were both fond of socializing over a drink or two. London by his professional writer days favored the cocktails of his day while Miller favored the crystal clear moonshine he first encountered in the mining camps. But I think this would have been a bridgeable gap. On the other hand they might have been competitors on the A Star is Bornmodel.
Miller considered himself a poet. It is significant that he published an edition of his complete poems but never produced an equivalent collection of his prose works in spite of the fact that he produced a sizable number of fiction and non-fiction work for magazines and newspapers. London on the other hand, concentrated his energies on his prose and a collection of his poetry had to wait til 2007. Miller took Byron as his model and celebrated aesthetics above all. London was a thoroughly commercial writer who made it a point of pride to crank out a thousand words a day.
It is interesting that they both participated in the Yukon gold rush in 1898. London went as one of the thousands looking to make their fortunes. Miller went as a reporter for various American newspapers. They both had struggles in that hard country. London came down with scurvy and Miller got his toes frostbitten. Both came home as soon as they were physically able to.
I recently read a number of London's Klondike stories and I found it heavy going. Perhaps some of the problem was reading a series of short stories all with the same setting but they began to seem monotonous after a while: Cold, Bleak, Dark, Cold, Everybody dies. Call of the Wild is definitely his best in this genre but it stands out. The other Yukon stories are not nearly as gripping. Miller wrote some serviceable pieces for the newspapers but the best thing to come out of his Yukon adventure was a strange and original poem titled The Yukon. You can read the poem here and decide for yourself who was better at mining Alaskan adventure for artistic gems.