Yes, the growths on your Dendrobium are Keikis and you should wait till roots appear at the base of the growths before you remove the Keikis. Your Dendrobium might be a Softcane/Nobile type which make keikis instead of blooms if given too much TLC in late autumn and winter.

Your Oncidium could use repotting. There are many You Tubes showing how to do it. I had mine for years and they didn't bloom. I found I was bringing them in too early in the winter. Now I don't bring them in until we are going to have a freeze. Almost all of them bloom every year now and I have at least a dozen.

Thank you both for all of that info! Yeah, both of my dendrobiums have a new growth at the base of the plant and keikis. I will watch them and snip them once they start sprouting roots.

I will repot my oncidium! Yay, now I have another one! Thanks for the advice on leaving them out, too. I am new to any orchid besides phalaenopsis or paphiopedilum, so it's been a steep learning curve with the oncidiums, dendrobiums, cattleya, and vandas.