If I use them as a dummy load for transmitters 144mhz and down, how bad would that be?
It's just a mismatched load, and the consequences are the same as for a mismatched antenna. Check your transmitter's manual for the degree of mismatch it can handle and any applicable warnings. Modern transmitters typically have self-protection circuits and will not be harmed, but may automatically reduce power or shut off.
Since they probably will seem like an inductive load, could I use capacitors to cancel out the inductance?
Yes, but it would be canceled out at a specific frequency only (and nearly canceled in a region around it) and would have some capacitive or inductive reactance elsewhere. That is, you now have a dummy load with a small bandwidth. If you want to use it on a particular band, or if the transmitter is capable of handling the SWR resulting from the mismatch, then this isn't a problem.
For comparison, if you instead construct your dummy load from non-inductive resistors, then you can use it at any frequency whatsoever equally well, at least ideally. In practice, there's always some stray inductance and/or capacitance and there will be limits — this is why manufactured dummy loads have specified frequency ranges.