It is just fine.
Yup. No problem at all.
FYI, the 75 ohm figure is NOT the cable's dc resistance, or its impedance at audio frequencies. It is what is called "characteristic impedance," which only comes into play at much higher frequencies, such as digital signals that have fast edge rates, or video or radio signals.
I agree with Kal and Al, especially with a high-quality baseband video or digital interconnect. However, if "75-ohm" means common CATV RG6 with crimped-on ends, then yes, this can very commonly be problematic . . . but this is not because of its 75-ohm impedance.
CATV RG6 and its connectors are optimized for frequencies above 50MHz, and are almost universally manufactured with the shield being aluminum foil in combination with partial-coverage aluminum-braid. This shield, in combined with the crimped-on connectors, leads to a much higher ground resistance than a good copper interconnect with soldered connectors. This might mean a couple ohms or more of resistance as opposed to a 1/10th ohm . . .
. . . which still doesn't seem like much, but if you have any ground-leakage current flowing from the AV receiver to the third-prong ground on the subwoofer (very common in a real-world installation) this can cause lots of hum, or switch-mode power-supply noise in the audio. Same goes for making hum bars appear in a baseband (i.e. component) video run across CATV RG6.
I bring this up because it seems that many "custom installation" companies use RG6 for just about everything, because it's a single kind of cable to keep on the truck, and damn near anybody can be trained to crimp on an RG6-style connector in well under 30 seconds.
Kirkus - two more issues I know of:
- coupled noise (in addition to ground loops) will cause voltage drops (returning to earth ground) appearing as a signal (since shield is used as a return - bad practice)
- cable is most likely made of low quality copper silver plated since signal at very high frequencies travels on the surface only.