Why you say the policy against mixing should be limited to chakra? In the page, it doesn't say it's specifically limited to that, does it? So it's safe to assume that the statement is applicable to any and all situations. Stating otherwise, it's a logical fallacy. I stand with Egon on this matter.
If you wish to use both, I suggest you split the working in two parts that you will do separately at different times during the day: one with the runes, one with Sanskrit. Sanskrit still raises your own energies, not external energies. This is unless you're using a planetary square/mantra, which instead invokes the energy of the planets. Moreover, runes create subtle connections between certain chakras for the energy to flow, while Sanskrit takes another approach.
I've never tried a working by using both runes and Sanskrit, so you are on your own.